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extern/asio-1.18.2/include/asio/execution/allocator.hpp

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+//
+// execution/allocator.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2021 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_EXECUTION_ALLOCATOR_HPP
+#define ASIO_EXECUTION_ALLOCATOR_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/detail/type_traits.hpp"
+#include "asio/execution/executor.hpp"
+#include "asio/execution/scheduler.hpp"
+#include "asio/execution/sender.hpp"
+#include "asio/is_applicable_property.hpp"
+#include "asio/traits/query_static_constexpr_member.hpp"
+#include "asio/traits/static_query.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+
+#if defined(GENERATING_DOCUMENTATION)
+
+namespace execution {
+
+/// A property to describe which allocator an executor will use to allocate the
+/// memory required to store a submitted function object.
+template <typename ProtoAllocator>
+struct allocator_t
+{
+  /// The allocator_t property applies to executors, senders, and schedulers.
+  template <typename T>
+  static constexpr bool is_applicable_property_v =
+    is_executor_v<T> || is_sender_v<T> || is_scheduler_v<T>;
+
+  /// The allocator_t property can be required.
+  static constexpr bool is_requirable = true;
+
+  /// The allocator_t property can be preferred.
+  static constexpr bool is_preferable = true;
+
+  /// Default constructor.
+  constexpr allocator_t();
+
+  /// Obtain the allocator stored in the allocator_t property object.
+  /**
+   * Present only if @c ProtoAllocator is non-void.
+   */
+  constexpr ProtoAllocator value() const;
+
+  /// Create an allocator_t object with a different allocator.
+  /**
+   * Present only if @c ProtoAllocator is void.
+   */
+  template <typename OtherAllocator>
+  allocator_t<OtherAllocator operator()(const OtherAllocator& a);
+};
+
+/// A special value used for accessing the allocator_t property.
+constexpr allocator_t<void> allocator;
+
+} // namespace execution
+
+#else // defined(GENERATING_DOCUMENTATION)
+
+namespace execution {
+
+template <typename ProtoAllocator>
+struct allocator_t
+{
+#if defined(ASIO_HAS_VARIABLE_TEMPLATES)
+  template <typename T>
+  ASIO_STATIC_CONSTEXPR(bool,
+    is_applicable_property_v = (
+      is_executor<T>::value
+        || conditional<
+            is_executor<T>::value,
+            false_type,
+            is_sender<T>
+          >::type::value
+        || conditional<
+            is_executor<T>::value,
+            false_type,
+            is_scheduler<T>
+          >::type::value));
+#endif // defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+  ASIO_STATIC_CONSTEXPR(bool, is_requirable = true);
+  ASIO_STATIC_CONSTEXPR(bool, is_preferable = true);
+
+  template <typename T>
+  struct static_proxy
+  {
+#if defined(ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
+    struct type
+    {
+      template <typename P>
+      static constexpr auto query(ASIO_MOVE_ARG(P) p)
+        noexcept(
+          noexcept(
+            conditional<true, T, P>::type::query(ASIO_MOVE_CAST(P)(p))
+          )
+        )
+        -> decltype(
+          conditional<true, T, P>::type::query(ASIO_MOVE_CAST(P)(p))
+        )
+      {
+        return T::query(ASIO_MOVE_CAST(P)(p));
+      }
+    };
+#else // defined(ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
+    typedef T type;
+#endif // defined(ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
+  };
+
+  template <typename T>
+  struct query_static_constexpr_member :
+    traits::query_static_constexpr_member<
+      typename static_proxy<T>::type, allocator_t> {};
+
+#if defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+  template <typename T>
+  static ASIO_CONSTEXPR
+  typename query_static_constexpr_member<T>::result_type
+  static_query()
+    ASIO_NOEXCEPT_IF((
+      query_static_constexpr_member<T>::is_noexcept))
+  {
+    return query_static_constexpr_member<T>::value();
+  }
+
+  template <typename E, typename T = decltype(allocator_t::static_query<E>())>
+  static ASIO_CONSTEXPR const T static_query_v
+    = allocator_t::static_query<E>();
+#endif // defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+  ASIO_CONSTEXPR ProtoAllocator value() const
+  {
+    return a_;
+  }
+
+private:
+  friend struct allocator_t<void>;
+
+  explicit ASIO_CONSTEXPR allocator_t(const ProtoAllocator& a)
+    : a_(a)
+  {
+  }
+
+  ProtoAllocator a_;
+};
+
+#if defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+template <typename ProtoAllocator> template <typename E, typename T>
+const T allocator_t<ProtoAllocator>::static_query_v;
+#endif // defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+template <>
+struct allocator_t<void>
+{
+#if defined(ASIO_HAS_VARIABLE_TEMPLATES)
+  template <typename T>
+  ASIO_STATIC_CONSTEXPR(bool,
+    is_applicable_property_v = (
+      is_executor<T>::value
+        || conditional<
+            is_executor<T>::value,
+            false_type,
+            is_sender<T>
+          >::type::value
+        || conditional<
+            is_executor<T>::value,
+            false_type,
+            is_scheduler<T>
+          >::type::value));
+#endif // defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+  ASIO_STATIC_CONSTEXPR(bool, is_requirable = true);
+  ASIO_STATIC_CONSTEXPR(bool, is_preferable = true);
+
+  ASIO_CONSTEXPR allocator_t()
+  {
+  }
+
+  template <typename T>
+  struct static_proxy
+  {
+#if defined(ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
+    struct type
+    {
+      template <typename P>
+      static constexpr auto query(ASIO_MOVE_ARG(P) p)
+        noexcept(
+          noexcept(
+            conditional<true, T, P>::type::query(ASIO_MOVE_CAST(P)(p))
+          )
+        )
+        -> decltype(
+          conditional<true, T, P>::type::query(ASIO_MOVE_CAST(P)(p))
+        )
+      {
+        return T::query(ASIO_MOVE_CAST(P)(p));
+      }
+    };
+#else // defined(ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
+    typedef T type;
+#endif // defined(ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
+  };
+
+  template <typename T>
+  struct query_static_constexpr_member :
+    traits::query_static_constexpr_member<
+      typename static_proxy<T>::type, allocator_t> {};
+
+#if defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+  template <typename T>
+  static ASIO_CONSTEXPR
+  typename query_static_constexpr_member<T>::result_type
+  static_query()
+    ASIO_NOEXCEPT_IF((
+      query_static_constexpr_member<T>::is_noexcept))
+  {
+    return query_static_constexpr_member<T>::value();
+  }
+
+  template <typename E, typename T = decltype(allocator_t::static_query<E>())>
+  static ASIO_CONSTEXPR const T static_query_v
+    = allocator_t::static_query<E>();
+#endif // defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+  template <typename OtherProtoAllocator>
+  ASIO_CONSTEXPR allocator_t<OtherProtoAllocator> operator()(
+      const OtherProtoAllocator& a) const
+  {
+    return allocator_t<OtherProtoAllocator>(a);
+  }
+};
+
+#if defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+template <typename E, typename T>
+const T allocator_t<void>::static_query_v;
+#endif // defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+#if defined(ASIO_HAS_CONSTEXPR) || defined(GENERATING_DOCUMENTATION)
+constexpr allocator_t<void> allocator;
+#else // defined(ASIO_HAS_CONSTEXPR) || defined(GENERATING_DOCUMENTATION)
+template <typename T>
+struct allocator_instance
+{
+  static allocator_t<T> instance;
+};
+
+template <typename T>
+allocator_t<T> allocator_instance<T>::instance;
+
+namespace {
+static const allocator_t<void>& allocator = allocator_instance<void>::instance;
+} // namespace
+#endif
+
+} // namespace execution
+
+#if !defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename T, typename ProtoAllocator>
+struct is_applicable_property<T, execution::allocator_t<ProtoAllocator> >
+  : integral_constant<bool,
+      execution::is_executor<T>::value
+        || conditional<
+            execution::is_executor<T>::value,
+            false_type,
+            execution::is_sender<T>
+          >::type::value
+        || conditional<
+            execution::is_executor<T>::value,
+            false_type,
+            execution::is_scheduler<T>
+          >::type::value>
+{
+};
+
+#endif // !defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+namespace traits {
+
+#if !defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  || !defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+template <typename T, typename ProtoAllocator>
+struct static_query<T, execution::allocator_t<ProtoAllocator>,
+  typename enable_if<
+    execution::allocator_t<ProtoAllocator>::template
+      query_static_constexpr_member<T>::is_valid
+  >::type>
+{
+  ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename execution::allocator_t<ProtoAllocator>::template
+    query_static_constexpr_member<T>::result_type result_type;
+
+  static ASIO_CONSTEXPR result_type value()
+  {
+    return execution::allocator_t<ProtoAllocator>::template
+      query_static_constexpr_member<T>::value();
+  }
+};
+
+#endif // !defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   || !defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+} // namespace traits
+
+#endif // defined(GENERATING_DOCUMENTATION)
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_EXECUTION_ALLOCATOR_HPP

extern/asio-1.18.2/include/asio/execution/bad_executor.hpp

@@ -0,0 +1,47 @@
+//
+// execution/bad_executor.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2021 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_EXECUTION_BAD_EXECUTOR_HPP
+#define ASIO_EXECUTION_BAD_EXECUTOR_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include <exception>
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace execution {
+
+/// Exception thrown when trying to access an empty polymorphic executor.
+class bad_executor
+  : public std::exception
+{
+public:
+  /// Constructor.
+  ASIO_DECL bad_executor() ASIO_NOEXCEPT;
+
+  /// Obtain message associated with exception.
+  ASIO_DECL virtual const char* what() const
+    ASIO_NOEXCEPT_OR_NOTHROW;
+};
+
+} // namespace execution
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#if defined(ASIO_HEADER_ONLY)
+# include "asio/execution/impl/bad_executor.ipp"
+#endif // defined(ASIO_HEADER_ONLY)
+
+#endif // ASIO_EXECUTION_BAD_EXECUTOR_HPP

extern/asio-1.18.2/include/asio/execution/bulk_execute.hpp

@@ -0,0 +1,395 @@
+//
+// execution/bulk_execute.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2021 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_EXECUTION_BULK_EXECUTE_HPP
+#define ASIO_EXECUTION_BULK_EXECUTE_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/detail/type_traits.hpp"
+#include "asio/execution/bulk_guarantee.hpp"
+#include "asio/execution/detail/bulk_sender.hpp"
+#include "asio/execution/executor.hpp"
+#include "asio/execution/sender.hpp"
+#include "asio/traits/bulk_execute_member.hpp"
+#include "asio/traits/bulk_execute_free.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+#if defined(GENERATING_DOCUMENTATION)
+
+namespace asio {
+namespace execution {
+
+/// A customisation point that creates a bulk sender.
+/**
+ * The name <tt>execution::bulk_execute</tt> denotes a customisation point
+ * object. If <tt>is_convertible_v<N, size_t></tt> is true, then the expression
+ * <tt>execution::bulk_execute(S, F, N)</tt> for some subexpressions
+ * <tt>S</tt>, <tt>F</tt>, and <tt>N</tt> is expression-equivalent to:
+ *
+ * @li <tt>S.bulk_execute(F, N)</tt>, if that expression is valid. If the
+ *   function selected does not execute <tt>N</tt> invocations of the function
+ *   object <tt>F</tt> on the executor <tt>S</tt> in bulk with forward progress
+ *   guarantee <tt>asio::query(S, execution::bulk_guarantee)</tt>, and
+ *   the result of that function does not model <tt>sender<void></tt>, the
+ *   program is ill-formed with no diagnostic required.
+ *
+ * @li Otherwise, <tt>bulk_execute(S, F, N)</tt>, if that expression is valid,
+ *   with overload resolution performed in a context that includes the
+ *   declaration <tt>void bulk_execute();</tt> and that does not include a
+ *   declaration of <tt>execution::bulk_execute</tt>. If the function selected
+ *   by overload resolution does not execute <tt>N</tt> invocations of the
+ *   function object <tt>F</tt> on the executor <tt>S</tt> in bulk with forward
+ *   progress guarantee <tt>asio::query(E,
+ *   execution::bulk_guarantee)</tt>, and the result of that function does not
+ *   model <tt>sender<void></tt>, the program is ill-formed with no diagnostic
+ *   required.
+ *
+ * @li Otherwise, if the types <tt>F</tt> and
+ *   <tt>executor_index_t<remove_cvref_t<S>></tt> model <tt>invocable</tt> and
+ *   if <tt>asio::query(S, execution::bulk_guarantee)</tt> equals
+ *   <tt>execution::bulk_guarantee.unsequenced</tt>, then
+ *
+ *    - Evaluates <tt>DECAY_COPY(std::forward<decltype(F)>(F))</tt> on the
+ *      calling thread to create a function object <tt>cf</tt>. [Note:
+ *      Additional copies of <tt>cf</tt> may subsequently be created. --end
+ *      note.]
+ *
+ *    - For each value of <tt>i</tt> in <tt>N</tt>, <tt>cf(i)</tt> (or copy of
+ *      <tt>cf</tt>)) will be invoked at most once by an execution agent that is
+ *      unique for each value of <tt>i</tt>.
+ *
+ *    - May block pending completion of one or more invocations of <tt>cf</tt>.
+ *
+ *    - Synchronizes with (C++Std [intro.multithread]) the invocations of
+ *      <tt>cf</tt>.
+ *
+ * @li Otherwise, <tt>execution::bulk_execute(S, F, N)</tt> is ill-formed.
+ */
+inline constexpr unspecified bulk_execute = unspecified;
+
+/// A type trait that determines whether a @c bulk_execute expression is
+/// well-formed.
+/**
+ * Class template @c can_bulk_execute is a trait that is derived from @c
+ * true_type if the expression <tt>execution::bulk_execute(std::declval<S>(),
+ * std::declval<F>(), std::declval<N>)</tt> is well formed; otherwise @c
+ * false_type.
+ */
+template <typename S, typename F, typename N>
+struct can_bulk_execute :
+  integral_constant<bool, automatically_determined>
+{
+};
+
+} // namespace execution
+} // namespace asio
+
+#else // defined(GENERATING_DOCUMENTATION)
+
+namespace asio_execution_bulk_execute_fn {
+
+using asio::declval;
+using asio::enable_if;
+using asio::execution::bulk_guarantee_t;
+using asio::execution::detail::bulk_sender;
+using asio::execution::executor_index;
+using asio::execution::is_sender;
+using asio::is_convertible;
+using asio::is_same;
+using asio::remove_cvref;
+using asio::result_of;
+using asio::traits::bulk_execute_free;
+using asio::traits::bulk_execute_member;
+using asio::traits::static_require;
+
+void bulk_execute();
+
+enum overload_type
+{
+  call_member,
+  call_free,
+  adapter,
+  ill_formed
+};
+
+template <typename S, typename Args, typename = void, typename = void,
+    typename = void, typename = void, typename = void, typename = void>
+struct call_traits
+{
+  ASIO_STATIC_CONSTEXPR(overload_type, overload = ill_formed);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef void result_type;
+};
+
+template <typename S, typename F, typename N>
+struct call_traits<S, void(F, N),
+  typename enable_if<
+    is_convertible<N, std::size_t>::value
+  >::type,
+  typename enable_if<
+    bulk_execute_member<S, F, N>::is_valid
+  >::type,
+  typename enable_if<
+    is_sender<
+      typename bulk_execute_member<S, F, N>::result_type
+    >::value
+  >::type> :
+  bulk_execute_member<S, F, N>
+{
+  ASIO_STATIC_CONSTEXPR(overload_type, overload = call_member);
+};
+
+template <typename S, typename F, typename N>
+struct call_traits<S, void(F, N),
+  typename enable_if<
+    is_convertible<N, std::size_t>::value
+  >::type,
+  typename enable_if<
+    !bulk_execute_member<S, F, N>::is_valid
+  >::type,
+  typename enable_if<
+    bulk_execute_free<S, F, N>::is_valid
+  >::type,
+  typename enable_if<
+    is_sender<
+      typename bulk_execute_free<S, F, N>::result_type
+    >::value
+  >::type> :
+  bulk_execute_free<S, F, N>
+{
+  ASIO_STATIC_CONSTEXPR(overload_type, overload = call_free);
+};
+
+template <typename S, typename F, typename N>
+struct call_traits<S, void(F, N),
+  typename enable_if<
+    is_convertible<N, std::size_t>::value
+  >::type,
+  typename enable_if<
+    !bulk_execute_member<S, F, N>::is_valid
+  >::type,
+  typename enable_if<
+    !bulk_execute_free<S, F, N>::is_valid
+  >::type,
+  typename enable_if<
+    is_sender<S>::value
+  >::type,
+  typename enable_if<
+    is_same<
+      typename result_of<
+        F(typename executor_index<typename remove_cvref<S>::type>::type)
+      >::type,
+      typename result_of<
+        F(typename executor_index<typename remove_cvref<S>::type>::type)
+      >::type
+    >::value
+  >::type,
+  typename enable_if<
+    static_require<S, bulk_guarantee_t::unsequenced_t>::is_valid
+  >::type>
+{
+  ASIO_STATIC_CONSTEXPR(overload_type, overload = adapter);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef bulk_sender<S, F, N> result_type;
+};
+
+struct impl
+{
+#if defined(ASIO_HAS_MOVE)
+  template <typename S, typename F, typename N>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<S, void(F, N)>::overload == call_member,
+    typename call_traits<S, void(F, N)>::result_type
+  >::type
+  operator()(S&& s, F&& f, N&& n) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<S, void(F, N)>::is_noexcept))
+  {
+    return ASIO_MOVE_CAST(S)(s).bulk_execute(
+        ASIO_MOVE_CAST(F)(f), ASIO_MOVE_CAST(N)(n));
+  }
+
+  template <typename S, typename F, typename N>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<S, void(F, N)>::overload == call_free,
+    typename call_traits<S, void(F, N)>::result_type
+  >::type
+  operator()(S&& s, F&& f, N&& n) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<S, void(F, N)>::is_noexcept))
+  {
+    return bulk_execute(ASIO_MOVE_CAST(S)(s),
+        ASIO_MOVE_CAST(F)(f), ASIO_MOVE_CAST(N)(n));
+  }
+
+  template <typename S, typename F, typename N>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<S, void(F, N)>::overload == adapter,
+    typename call_traits<S, void(F, N)>::result_type
+  >::type
+  operator()(S&& s, F&& f, N&& n) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<S, void(F, N)>::is_noexcept))
+  {
+    return typename call_traits<S, void(F, N)>::result_type(
+        ASIO_MOVE_CAST(S)(s), ASIO_MOVE_CAST(F)(f),
+        ASIO_MOVE_CAST(N)(n));
+  }
+#else // defined(ASIO_HAS_MOVE)
+  template <typename S, typename F, typename N>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<S, void(const F&, const N&)>::overload == call_member,
+    typename call_traits<S, void(const F&, const N&)>::result_type
+  >::type
+  operator()(S& s, const F& f, const N& n) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<S, void(const F&, const N&)>::is_noexcept))
+  {
+    return s.bulk_execute(ASIO_MOVE_CAST(F)(f),
+        ASIO_MOVE_CAST(N)(n));
+  }
+
+  template <typename S, typename F, typename N>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<S, void(const F&, const N&)>::overload == call_member,
+    typename call_traits<S, void(const F&, const N&)>::result_type
+  >::type
+  operator()(const S& s, const F& f, const N& n) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<S, void(const F&, const N&)>::is_noexcept))
+  {
+    return s.bulk_execute(ASIO_MOVE_CAST(F)(f),
+        ASIO_MOVE_CAST(N)(n));
+  }
+
+  template <typename S, typename F, typename N>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<S, void(const F&, const N&)>::overload == call_free,
+    typename call_traits<S, void(const F&, const N&)>::result_type
+  >::type
+  operator()(S& s, const F& f, const N& n) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<S, void(const F&, const N&)>::is_noexcept))
+  {
+    return bulk_execute(s, ASIO_MOVE_CAST(F)(f),
+        ASIO_MOVE_CAST(N)(n));
+  }
+
+  template <typename S, typename F, typename N>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<S, void(const F&, const N&)>::overload == call_free,
+    typename call_traits<S, void(const F&, const N&)>::result_type
+  >::type
+  operator()(const S& s, const F& f, const N& n) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<S, void(const F&, const N&)>::is_noexcept))
+  {
+    return bulk_execute(s, ASIO_MOVE_CAST(F)(f),
+        ASIO_MOVE_CAST(N)(n));
+  }
+
+  template <typename S, typename F, typename N>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<S, void(const F&, const N&)>::overload == adapter,
+    typename call_traits<S, void(const F&, const N&)>::result_type
+  >::type
+  operator()(S& s, const F& f, const N& n) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<S, void(const F&, const N&)>::is_noexcept))
+  {
+    return typename call_traits<S, void(const F&, const N&)>::result_type(
+        s, ASIO_MOVE_CAST(F)(f), ASIO_MOVE_CAST(N)(n));
+  }
+
+  template <typename S, typename F, typename N>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<S, void(const F&, const N&)>::overload == adapter,
+    typename call_traits<S, void(const F&, const N&)>::result_type
+  >::type
+  operator()(const S& s, const F& f, const N& n) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<S, void(const F&, const N&)>::is_noexcept))
+  {
+    return typename call_traits<S, void(const F&, const N&)>::result_type(
+        s, ASIO_MOVE_CAST(F)(f), ASIO_MOVE_CAST(N)(n));
+  }
+#endif // defined(ASIO_HAS_MOVE)
+};
+
+template <typename T = impl>
+struct static_instance
+{
+  static const T instance;
+};
+
+template <typename T>
+const T static_instance<T>::instance = {};
+
+} // namespace asio_execution_bulk_execute_fn
+namespace asio {
+namespace execution {
+namespace {
+
+static ASIO_CONSTEXPR
+  const asio_execution_bulk_execute_fn::impl& bulk_execute =
+    asio_execution_bulk_execute_fn::static_instance<>::instance;
+
+} // namespace
+
+template <typename S, typename F, typename N>
+struct can_bulk_execute :
+  integral_constant<bool,
+    asio_execution_bulk_execute_fn::call_traits<S, void(F, N)>::overload !=
+      asio_execution_bulk_execute_fn::ill_formed>
+{
+};
+
+#if defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename S, typename F, typename N>
+constexpr bool can_bulk_execute_v = can_bulk_execute<S, F, N>::value;
+
+#endif // defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename S, typename F, typename N>
+struct is_nothrow_bulk_execute :
+  integral_constant<bool,
+    asio_execution_bulk_execute_fn::call_traits<S, void(F, N)>::is_noexcept>
+{
+};
+
+#if defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename S, typename F, typename N>
+constexpr bool is_nothrow_bulk_execute_v
+  = is_nothrow_bulk_execute<S, F, N>::value;
+
+#endif // defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename S, typename F, typename N>
+struct bulk_execute_result
+{
+  typedef typename asio_execution_bulk_execute_fn::call_traits<
+      S, void(F, N)>::result_type type;
+};
+
+} // namespace execution
+} // namespace asio
+
+#endif // defined(GENERATING_DOCUMENTATION)
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_EXECUTION_BULK_EXECUTE_HPP

extern/asio-1.18.2/include/asio/execution/connect.hpp

@@ -0,0 +1,489 @@
+//
+// execution/connect.hpp
+// ~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2021 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_EXECUTION_CONNECT_HPP
+#define ASIO_EXECUTION_CONNECT_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/detail/type_traits.hpp"
+#include "asio/execution/detail/as_invocable.hpp"
+#include "asio/execution/detail/as_operation.hpp"
+#include "asio/execution/detail/as_receiver.hpp"
+#include "asio/execution/executor.hpp"
+#include "asio/execution/operation_state.hpp"
+#include "asio/execution/receiver.hpp"
+#include "asio/execution/sender.hpp"
+#include "asio/traits/connect_member.hpp"
+#include "asio/traits/connect_free.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+#if defined(GENERATING_DOCUMENTATION)
+
+namespace asio {
+namespace execution {
+
+/// A customisation point that connects a sender to a receiver.
+/**
+ * The name <tt>execution::connect</tt> denotes a customisation point object.
+ * For some subexpressions <tt>s</tt> and <tt>r</tt>, let <tt>S</tt> be a type
+ * such that <tt>decltype((s))</tt> is <tt>S</tt> and let <tt>R</tt> be a type
+ * such that <tt>decltype((r))</tt> is <tt>R</tt>. The expression
+ * <tt>execution::connect(s, r)</tt> is expression-equivalent to:
+ *
+ * @li <tt>s.connect(r)</tt>, if that expression is valid, if its type
+ *   satisfies <tt>operation_state</tt>, and if <tt>S</tt> satisfies
+ *   <tt>sender</tt>.
+ *
+ * @li Otherwise, <tt>connect(s, r)</tt>, if that expression is valid, if its
+ *   type satisfies <tt>operation_state</tt>, and if <tt>S</tt> satisfies
+ *   <tt>sender</tt>, with overload resolution performed in a context that
+ *   includes the declaration <tt>void connect();</tt> and that does not include
+ *   a declaration of <tt>execution::connect</tt>.
+ *
+ * @li Otherwise, <tt>as_operation{s, r}</tt>, if <tt>r</tt> is not an instance
+ *  of <tt>as_receiver<F, S></tt> for some type <tt>F</tt>, and if
+ *  <tt>receiver_of<R> && executor_of<remove_cvref_t<S>,
+ *  as_invocable<remove_cvref_t<R>, S>></tt> is <tt>true</tt>, where
+ *  <tt>as_operation</tt> is an implementation-defined class equivalent to
+ *  @code template <class S, class R>
+ *  struct as_operation
+ *  {
+ *    remove_cvref_t<S> e_;
+ *    remove_cvref_t<R> r_;
+ *    void start() noexcept try {
+ *      execution::execute(std::move(e_),
+ *          as_invocable<remove_cvref_t<R>, S>{r_});
+ *    } catch(...) {
+ *      execution::set_error(std::move(r_), current_exception());
+ *    }
+ *  }; @endcode
+ *  and <tt>as_invocable</tt> is a class template equivalent to the following:
+ *  @code template<class R>
+ *  struct as_invocable
+ *  {
+ *    R* r_;
+ *    explicit as_invocable(R& r) noexcept
+ *      : r_(std::addressof(r)) {}
+ *    as_invocable(as_invocable && other) noexcept
+ *      : r_(std::exchange(other.r_, nullptr)) {}
+ *    ~as_invocable() {
+ *      if(r_)
+ *        execution::set_done(std::move(*r_));
+ *    }
+ *    void operator()() & noexcept try {
+ *      execution::set_value(std::move(*r_));
+ *      r_ = nullptr;
+ *    } catch(...) {
+ *      execution::set_error(std::move(*r_), current_exception());
+ *      r_ = nullptr;
+ *    }
+ *  };
+ *  @endcode
+ *
+ * @li Otherwise, <tt>execution::connect(s, r)</tt> is ill-formed.
+ */
+inline constexpr unspecified connect = unspecified;
+
+/// A type trait that determines whether a @c connect expression is
+/// well-formed.
+/**
+ * Class template @c can_connect is a trait that is derived from
+ * @c true_type if the expression <tt>execution::connect(std::declval<S>(),
+ * std::declval<R>())</tt> is well formed; otherwise @c false_type.
+ */
+template <typename S, typename R>
+struct can_connect :
+  integral_constant<bool, automatically_determined>
+{
+};
+
+/// A type trait to determine the result of a @c connect expression.
+template <typename S, typename R>
+struct connect_result
+{
+  /// The type of the connect expression.
+  /**
+   * The type of the expression <tt>execution::connect(std::declval<S>(),
+   * std::declval<R>())</tt>.
+   */
+  typedef automatically_determined type;
+};
+
+/// A type alis to determine the result of a @c connect expression.
+template <typename S, typename R>
+using connect_result_t = typename connect_result<S, R>::type;
+
+} // namespace execution
+} // namespace asio
+
+#else // defined(GENERATING_DOCUMENTATION)
+
+namespace asio_execution_connect_fn {
+
+using asio::conditional;
+using asio::declval;
+using asio::enable_if;
+using asio::execution::detail::as_invocable;
+using asio::execution::detail::as_operation;
+using asio::execution::detail::is_as_receiver;
+using asio::execution::is_executor_of;
+using asio::execution::is_operation_state;
+using asio::execution::is_receiver;
+using asio::execution::is_sender;
+using asio::false_type;
+using asio::remove_cvref;
+using asio::traits::connect_free;
+using asio::traits::connect_member;
+
+void connect();
+
+enum overload_type
+{
+  call_member,
+  call_free,
+  adapter,
+  ill_formed
+};
+
+template <typename S, typename R, typename = void,
+   typename = void, typename = void, typename = void>
+struct call_traits
+{
+  ASIO_STATIC_CONSTEXPR(overload_type, overload = ill_formed);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef void result_type;
+};
+
+template <typename S, typename R>
+struct call_traits<S, void(R),
+  typename enable_if<
+    connect_member<S, R>::is_valid
+  >::type,
+  typename enable_if<
+    is_operation_state<typename connect_member<S, R>::result_type>::value
+  >::type,
+  typename enable_if<
+    is_sender<typename remove_cvref<S>::type>::value
+  >::type> :
+  connect_member<S, R>
+{
+  ASIO_STATIC_CONSTEXPR(overload_type, overload = call_member);
+};
+
+template <typename S, typename R>
+struct call_traits<S, void(R),
+  typename enable_if<
+    !connect_member<S, R>::is_valid
+  >::type,
+  typename enable_if<
+    connect_free<S, R>::is_valid
+  >::type,
+  typename enable_if<
+    is_operation_state<typename connect_free<S, R>::result_type>::value
+  >::type,
+  typename enable_if<
+    is_sender<typename remove_cvref<S>::type>::value
+  >::type> :
+  connect_free<S, R>
+{
+  ASIO_STATIC_CONSTEXPR(overload_type, overload = call_free);
+};
+
+template <typename S, typename R>
+struct call_traits<S, void(R),
+  typename enable_if<
+    !connect_member<S, R>::is_valid
+  >::type,
+  typename enable_if<
+    !connect_free<S, R>::is_valid
+  >::type,
+  typename enable_if<
+    is_receiver<R>::value
+  >::type,
+  typename enable_if<
+    conditional<
+      !is_as_receiver<
+        typename remove_cvref<R>::type
+      >::value,
+      is_executor_of<
+        typename remove_cvref<S>::type,
+        as_invocable<typename remove_cvref<R>::type, S>
+      >,
+      false_type
+    >::type::value
+  >::type>
+{
+  ASIO_STATIC_CONSTEXPR(overload_type, overload = adapter);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef as_operation<S, R> result_type;
+};
+
+struct impl
+{
+#if defined(ASIO_HAS_MOVE)
+  template <typename S, typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<S, void(R)>::overload == call_member,
+    typename call_traits<S, void(R)>::result_type
+  >::type
+  operator()(S&& s, R&& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<S, void(R)>::is_noexcept))
+  {
+    return ASIO_MOVE_CAST(S)(s).connect(ASIO_MOVE_CAST(R)(r));
+  }
+
+  template <typename S, typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<S, void(R)>::overload == call_free,
+    typename call_traits<S, void(R)>::result_type
+  >::type
+  operator()(S&& s, R&& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<S, void(R)>::is_noexcept))
+  {
+    return connect(ASIO_MOVE_CAST(S)(s), ASIO_MOVE_CAST(R)(r));
+  }
+
+  template <typename S, typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<S, void(R)>::overload == adapter,
+    typename call_traits<S, void(R)>::result_type
+  >::type
+  operator()(S&& s, R&& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<S, void(R)>::is_noexcept))
+  {
+    return typename call_traits<S, void(R)>::result_type(
+        ASIO_MOVE_CAST(S)(s), ASIO_MOVE_CAST(R)(r));
+  }
+#else // defined(ASIO_HAS_MOVE)
+  template <typename S, typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<S&, void(R&)>::overload == call_member,
+    typename call_traits<S&, void(R&)>::result_type
+  >::type
+  operator()(S& s, R& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<S&, void(R&)>::is_noexcept))
+  {
+    return s.connect(r);
+  }
+
+  template <typename S, typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<const S&, void(R&)>::overload == call_member,
+    typename call_traits<const S&, void(R&)>::result_type
+  >::type
+  operator()(const S& s, R& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<const S&, void(R&)>::is_noexcept))
+  {
+    return s.connect(r);
+  }
+
+  template <typename S, typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<S&, void(R&)>::overload == call_free,
+    typename call_traits<S&, void(R&)>::result_type
+  >::type
+  operator()(S& s, R& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<S&, void(R&)>::is_noexcept))
+  {
+    return connect(s, r);
+  }
+
+  template <typename S, typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<const S&, void(R&)>::overload == call_free,
+    typename call_traits<const S&, void(R&)>::result_type
+  >::type
+  operator()(const S& s, R& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<const S&, void(R&)>::is_noexcept))
+  {
+    return connect(s, r);
+  }
+
+  template <typename S, typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<S&, void(R&)>::overload == adapter,
+    typename call_traits<S&, void(R&)>::result_type
+  >::type
+  operator()(S& s, R& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<S&, void(R&)>::is_noexcept))
+  {
+    return typename call_traits<S&, void(R&)>::result_type(s, r);
+  }
+
+  template <typename S, typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<const S&, void(R&)>::overload == adapter,
+    typename call_traits<const S&, void(R&)>::result_type
+  >::type
+  operator()(const S& s, R& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<const S&, void(R&)>::is_noexcept))
+  {
+    return typename call_traits<const S&, void(R&)>::result_type(s, r);
+  }
+
+  template <typename S, typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<S&, void(const R&)>::overload == call_member,
+    typename call_traits<S&, void(const R&)>::result_type
+  >::type
+  operator()(S& s, const R& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<S&, void(const R&)>::is_noexcept))
+  {
+    return s.connect(r);
+  }
+
+  template <typename S, typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<const S&, void(const R&)>::overload == call_member,
+    typename call_traits<const S&, void(const R&)>::result_type
+  >::type
+  operator()(const S& s, const R& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<const S&, void(const R&)>::is_noexcept))
+  {
+    return s.connect(r);
+  }
+
+  template <typename S, typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<S&, void(const R&)>::overload == call_free,
+    typename call_traits<S&, void(const R&)>::result_type
+  >::type
+  operator()(S& s, const R& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<S&, void(const R&)>::is_noexcept))
+  {
+    return connect(s, r);
+  }
+
+  template <typename S, typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<const S&, void(const R&)>::overload == call_free,
+    typename call_traits<const S&, void(const R&)>::result_type
+  >::type
+  operator()(const S& s, const R& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<const S&, void(const R&)>::is_noexcept))
+  {
+    return connect(s, r);
+  }
+
+  template <typename S, typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<S&, void(const R&)>::overload == adapter,
+    typename call_traits<S&, void(const R&)>::result_type
+  >::type
+  operator()(S& s, const R& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<S&, void(const R&)>::is_noexcept))
+  {
+    return typename call_traits<S&, void(const R&)>::result_type(s, r);
+  }
+
+  template <typename S, typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<const S&, void(const R&)>::overload == adapter,
+    typename call_traits<const S&, void(const R&)>::result_type
+  >::type
+  operator()(const S& s, const R& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<const S&, void(const R&)>::is_noexcept))
+  {
+    return typename call_traits<const S&, void(const R&)>::result_type(s, r);
+  }
+#endif // defined(ASIO_HAS_MOVE)
+};
+
+template <typename T = impl>
+struct static_instance
+{
+  static const T instance;
+};
+
+template <typename T>
+const T static_instance<T>::instance = {};
+
+} // namespace asio_execution_connect_fn
+namespace asio {
+namespace execution {
+namespace {
+
+static ASIO_CONSTEXPR const asio_execution_connect_fn::impl&
+  connect = asio_execution_connect_fn::static_instance<>::instance;
+
+} // namespace
+
+template <typename S, typename R>
+struct can_connect :
+  integral_constant<bool,
+    asio_execution_connect_fn::call_traits<S, void(R)>::overload !=
+      asio_execution_connect_fn::ill_formed>
+{
+};
+
+#if defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename S, typename R>
+constexpr bool can_connect_v = can_connect<S, R>::value;
+
+#endif // defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename S, typename R>
+struct is_nothrow_connect :
+  integral_constant<bool,
+    asio_execution_connect_fn::call_traits<S, void(R)>::is_noexcept>
+{
+};
+
+#if defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename S, typename R>
+constexpr bool is_nothrow_connect_v
+  = is_nothrow_connect<S, R>::value;
+
+#endif // defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename S, typename R>
+struct connect_result
+{
+  typedef typename asio_execution_connect_fn::call_traits<
+      S, void(R)>::result_type type;
+};
+
+#if defined(ASIO_HAS_ALIAS_TEMPLATES)
+
+template <typename S, typename R>
+using connect_result_t = typename connect_result<S, R>::type;
+
+#endif // defined(ASIO_HAS_ALIAS_TEMPLATES)
+
+} // namespace execution
+} // namespace asio
+
+#endif // defined(GENERATING_DOCUMENTATION)
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_EXECUTION_CONNECT_HPP

extern/asio-1.18.2/include/asio/execution/context.hpp

@@ -0,0 +1,233 @@
+//
+// execution/context.hpp
+// ~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2021 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_EXECUTION_CONTEXT2_HPP
+#define ASIO_EXECUTION_CONTEXT2_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/detail/type_traits.hpp"
+#include "asio/execution/executor.hpp"
+#include "asio/execution/scheduler.hpp"
+#include "asio/execution/sender.hpp"
+#include "asio/is_applicable_property.hpp"
+#include "asio/traits/query_static_constexpr_member.hpp"
+#include "asio/traits/static_query.hpp"
+
+#if defined(ASIO_HAS_STD_ANY)
+# include <any>
+#endif // defined(ASIO_HAS_STD_ANY)
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+
+#if defined(GENERATING_DOCUMENTATION)
+
+namespace execution {
+
+/// A property that is used to obtain the execution context that is associated
+/// with an executor.
+struct context_t
+{
+  /// The context_t property applies to executors, senders, and schedulers.
+  template <typename T>
+  static constexpr bool is_applicable_property_v =
+    is_executor_v<T> || is_sender_v<T> || is_scheduler_v<T>;
+
+  /// The context_t property cannot be required.
+  static constexpr bool is_requirable = false;
+
+  /// The context_t property cannot be preferred.
+  static constexpr bool is_preferable = false;
+
+  /// The type returned by queries against an @c any_executor.
+  typedef std::any polymorphic_query_result_type;
+};
+
+/// A special value used for accessing the context_t property.
+constexpr context_t context;
+
+} // namespace execution
+
+#else // defined(GENERATING_DOCUMENTATION)
+
+namespace execution {
+namespace detail {
+
+template <int I = 0>
+struct context_t
+{
+#if defined(ASIO_HAS_VARIABLE_TEMPLATES)
+  template <typename T>
+  ASIO_STATIC_CONSTEXPR(bool,
+    is_applicable_property_v = (
+      is_executor<T>::value
+        || conditional<
+            is_executor<T>::value,
+            false_type,
+            is_sender<T>
+          >::type::value
+        || conditional<
+            is_executor<T>::value,
+            false_type,
+            is_scheduler<T>
+          >::type::value));
+#endif // defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+  ASIO_STATIC_CONSTEXPR(bool, is_requirable = false);
+  ASIO_STATIC_CONSTEXPR(bool, is_preferable = false);
+
+#if defined(ASIO_HAS_STD_ANY)
+  typedef std::any polymorphic_query_result_type;
+#endif // defined(ASIO_HAS_STD_ANY)
+
+  ASIO_CONSTEXPR context_t()
+  {
+  }
+
+  template <typename T>
+  struct static_proxy
+  {
+#if defined(ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
+    struct type
+    {
+      template <typename P>
+      static constexpr auto query(ASIO_MOVE_ARG(P) p)
+        noexcept(
+          noexcept(
+            conditional<true, T, P>::type::query(ASIO_MOVE_CAST(P)(p))
+          )
+        )
+        -> decltype(
+          conditional<true, T, P>::type::query(ASIO_MOVE_CAST(P)(p))
+        )
+      {
+        return T::query(ASIO_MOVE_CAST(P)(p));
+      }
+    };
+#else // defined(ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
+    typedef T type;
+#endif // defined(ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
+  };
+
+  template <typename T>
+  struct query_static_constexpr_member :
+    traits::query_static_constexpr_member<
+      typename static_proxy<T>::type, context_t> {};
+
+#if defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+  template <typename T>
+  static ASIO_CONSTEXPR
+  typename query_static_constexpr_member<T>::result_type
+  static_query()
+    ASIO_NOEXCEPT_IF((
+      query_static_constexpr_member<T>::is_noexcept))
+  {
+    return query_static_constexpr_member<T>::value();
+  }
+
+  template <typename E, typename T = decltype(context_t::static_query<E>())>
+  static ASIO_CONSTEXPR const T static_query_v
+    = context_t::static_query<E>();
+#endif // defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+#if !defined(ASIO_HAS_CONSTEXPR)
+  static const context_t instance;
+#endif // !defined(ASIO_HAS_CONSTEXPR)
+};
+
+#if defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+template <int I> template <typename E, typename T>
+const T context_t<I>::static_query_v;
+#endif // defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+#if !defined(ASIO_HAS_CONSTEXPR)
+template <int I>
+const context_t<I> context_t<I>::instance;
+#endif
+
+} // namespace detail
+
+typedef detail::context_t<> context_t;
+
+#if defined(ASIO_HAS_CONSTEXPR) || defined(GENERATING_DOCUMENTATION)
+constexpr context_t context;
+#else // defined(ASIO_HAS_CONSTEXPR) || defined(GENERATING_DOCUMENTATION)
+namespace { static const context_t& context = context_t::instance; }
+#endif
+
+} // namespace execution
+
+#if !defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename T>
+struct is_applicable_property<T, execution::context_t>
+  : integral_constant<bool,
+      execution::is_executor<T>::value
+        || conditional<
+            execution::is_executor<T>::value,
+            false_type,
+            execution::is_sender<T>
+          >::type::value
+        || conditional<
+            execution::is_executor<T>::value,
+            false_type,
+            execution::is_scheduler<T>
+          >::type::value>
+{
+};
+
+#endif // !defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+namespace traits {
+
+#if !defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  || !defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+template <typename T>
+struct static_query<T, execution::context_t,
+  typename enable_if<
+    execution::detail::context_t<0>::
+      query_static_constexpr_member<T>::is_valid
+  >::type>
+{
+  ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename execution::detail::context_t<0>::
+    query_static_constexpr_member<T>::result_type result_type;
+
+  static ASIO_CONSTEXPR result_type value()
+  {
+    return execution::detail::context_t<0>::
+      query_static_constexpr_member<T>::value();
+  }
+};
+
+#endif // !defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   || !defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+} // namespace traits
+
+#endif // defined(GENERATING_DOCUMENTATION)
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_EXECUTION_CONTEXT2_HPP

extern/asio-1.18.2/include/asio/execution/context_as.hpp

@@ -0,0 +1,221 @@
+//
+// execution/context_as.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2021 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_EXECUTION_CONTEXT_AS_HPP
+#define ASIO_EXECUTION_CONTEXT_AS_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/detail/type_traits.hpp"
+#include "asio/execution/context.hpp"
+#include "asio/execution/executor.hpp"
+#include "asio/execution/scheduler.hpp"
+#include "asio/execution/sender.hpp"
+#include "asio/is_applicable_property.hpp"
+#include "asio/query.hpp"
+#include "asio/traits/query_static_constexpr_member.hpp"
+#include "asio/traits/static_query.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+
+#if defined(GENERATING_DOCUMENTATION)
+
+namespace execution {
+
+/// A property that is used to obtain the execution context that is associated
+/// with an executor.
+template <typename U>
+struct context_as_t
+{
+  /// The context_as_t property applies to executors, senders, and schedulers.
+  template <typename T>
+  static constexpr bool is_applicable_property_v =
+    is_executor_v<T> || is_sender_v<T> || is_scheduler_v<T>;
+
+  /// The context_t property cannot be required.
+  static constexpr bool is_requirable = false;
+
+  /// The context_t property cannot be preferred.
+  static constexpr bool is_preferable = false;
+
+  /// The type returned by queries against an @c any_executor.
+  typedef T polymorphic_query_result_type;
+};
+
+/// A special value used for accessing the context_as_t property.
+template <typename U>
+constexpr context_as_t context_as;
+
+} // namespace execution
+
+#else // defined(GENERATING_DOCUMENTATION)
+
+namespace execution {
+
+template <typename T>
+struct context_as_t
+{
+#if defined(ASIO_HAS_VARIABLE_TEMPLATES)
+  template <typename U>
+  ASIO_STATIC_CONSTEXPR(bool,
+    is_applicable_property_v = (
+      is_executor<U>::value
+        || conditional<
+            is_executor<U>::value,
+            false_type,
+            is_sender<U>
+          >::type::value
+        || conditional<
+            is_executor<U>::value,
+            false_type,
+            is_scheduler<U>
+          >::type::value));
+#endif // defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+  ASIO_STATIC_CONSTEXPR(bool, is_requirable = false);
+  ASIO_STATIC_CONSTEXPR(bool, is_preferable = false);
+
+  typedef T polymorphic_query_result_type;
+
+  ASIO_CONSTEXPR context_as_t()
+  {
+  }
+
+  ASIO_CONSTEXPR context_as_t(context_t)
+  {
+  }
+
+#if defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+  template <typename E>
+  static ASIO_CONSTEXPR
+  typename context_t::query_static_constexpr_member<E>::result_type
+  static_query()
+    ASIO_NOEXCEPT_IF((
+      context_t::query_static_constexpr_member<E>::is_noexcept))
+  {
+    return context_t::query_static_constexpr_member<E>::value();
+  }
+
+  template <typename E, typename U = decltype(context_as_t::static_query<E>())>
+  static ASIO_CONSTEXPR const U static_query_v
+    = context_as_t::static_query<E>();
+#endif // defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+  template <typename Executor, typename U>
+  friend ASIO_CONSTEXPR U query(
+      const Executor& ex, const context_as_t<U>&,
+      typename enable_if<
+        is_same<T, U>::value
+      >::type* = 0,
+      typename enable_if<
+        can_query<const Executor&, const context_t&>::value
+      >::type* = 0)
+#if !defined(__clang__) // Clang crashes if noexcept is used here.
+#if defined(ASIO_MSVC) // Visual C++ wants the type to be qualified.
+    ASIO_NOEXCEPT_IF((
+      is_nothrow_query<const Executor&, const context_t&>::value))
+#else // defined(ASIO_MSVC)
+    ASIO_NOEXCEPT_IF((
+      is_nothrow_query<const Executor&, const context_t&>::value))
+#endif // defined(ASIO_MSVC)
+#endif // !defined(__clang__)
+  {
+    return asio::query(ex, context);
+  }
+};
+
+#if defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+template <typename T> template <typename E, typename U>
+const U context_as_t<T>::static_query_v;
+#endif // defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+#if (defined(ASIO_HAS_VARIABLE_TEMPLATES) \
+    && defined(ASIO_HAS_CONSTEXPR)) \
+  || defined(GENERATING_DOCUMENTATION)
+template <typename T>
+constexpr context_as_t<T> context_as{};
+#endif // (defined(ASIO_HAS_VARIABLE_TEMPLATES)
+       //     && defined(ASIO_HAS_CONSTEXPR))
+       //   || defined(GENERATING_DOCUMENTATION)
+
+} // namespace execution
+
+#if !defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename T, typename U>
+struct is_applicable_property<T, execution::context_as_t<U> >
+  : integral_constant<bool,
+      execution::is_executor<T>::value
+        || conditional<
+            execution::is_executor<T>::value,
+            false_type,
+            execution::is_sender<T>
+          >::type::value
+        || conditional<
+            execution::is_executor<T>::value,
+            false_type,
+            execution::is_scheduler<T>
+          >::type::value>
+{
+};
+
+#endif // !defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+namespace traits {
+
+#if !defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  || !defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+template <typename T, typename U>
+struct static_query<T, execution::context_as_t<U>,
+  typename enable_if<
+    static_query<T, execution::context_t>::is_valid
+  >::type> : static_query<T, execution::context_t>
+{
+};
+
+#endif // !defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   || !defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+#if !defined(ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+template <typename T, typename U>
+struct query_free<T, execution::context_as_t<U>,
+    typename enable_if<
+      can_query<const T&, const execution::context_t&>::value
+    >::type>
+{
+  ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept =
+    (is_nothrow_query<const T&, const execution::context_t&>::value));
+
+  typedef U result_type;
+};
+
+#endif // !defined(ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+} // namespace traits
+
+#endif // defined(GENERATING_DOCUMENTATION)
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_EXECUTION_CONTEXT_AS_HPP

extern/asio-1.18.2/include/asio/execution/detail/as_invocable.hpp

@@ -0,0 +1,152 @@
+//
+// execution/detail/as_invocable.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2021 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_EXECUTION_DETAIL_AS_INVOCABLE_HPP
+#define ASIO_EXECUTION_DETAIL_AS_INVOCABLE_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/detail/atomic_count.hpp"
+#include "asio/detail/memory.hpp"
+#include "asio/detail/type_traits.hpp"
+#include "asio/execution/receiver_invocation_error.hpp"
+#include "asio/execution/set_done.hpp"
+#include "asio/execution/set_error.hpp"
+#include "asio/execution/set_value.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace execution {
+namespace detail {
+
+#if defined(ASIO_HAS_MOVE)
+
+template <typename Receiver, typename>
+struct as_invocable
+{
+  Receiver* receiver_;
+
+  explicit as_invocable(Receiver& r) ASIO_NOEXCEPT
+    : receiver_(asio::detail::addressof(r))
+  {
+  }
+
+  as_invocable(as_invocable&& other) ASIO_NOEXCEPT
+    : receiver_(other.receiver_)
+  {
+    other.receiver_ = 0;
+  }
+
+  ~as_invocable()
+  {
+    if (receiver_)
+      execution::set_done(ASIO_MOVE_OR_LVALUE(Receiver)(*receiver_));
+  }
+
+  void operator()() ASIO_LVALUE_REF_QUAL ASIO_NOEXCEPT
+  {
+#if !defined(ASIO_NO_EXCEPTIONS)
+    try
+    {
+#endif // !defined(ASIO_NO_EXCEPTIONS)
+      execution::set_value(ASIO_MOVE_CAST(Receiver)(*receiver_));
+      receiver_ = 0;
+#if !defined(ASIO_NO_EXCEPTIONS)
+    }
+    catch (...)
+    {
+#if defined(ASIO_HAS_STD_EXCEPTION_PTR)
+      execution::set_error(ASIO_MOVE_CAST(Receiver)(*receiver_),
+          std::make_exception_ptr(receiver_invocation_error()));
+      receiver_ = 0;
+#else // defined(ASIO_HAS_STD_EXCEPTION_PTR)
+      std::terminate();
+#endif // defined(ASIO_HAS_STD_EXCEPTION_PTR)
+    }
+#endif // !defined(ASIO_NO_EXCEPTIONS)
+  }
+};
+
+#else // defined(ASIO_HAS_MOVE)
+
+template <typename Receiver, typename>
+struct as_invocable
+{
+  Receiver* receiver_;
+  asio::detail::shared_ptr<asio::detail::atomic_count> ref_count_;
+
+  explicit as_invocable(Receiver& r,
+      const asio::detail::shared_ptr<
+        asio::detail::atomic_count>& c) ASIO_NOEXCEPT
+    : receiver_(asio::detail::addressof(r)),
+      ref_count_(c)
+  {
+  }
+
+  as_invocable(const as_invocable& other) ASIO_NOEXCEPT
+    : receiver_(other.receiver_),
+      ref_count_(other.ref_count_)
+  {
+    ++(*ref_count_);
+  }
+
+  ~as_invocable()
+  {
+    if (--(*ref_count_) == 0)
+      execution::set_done(*receiver_);
+  }
+
+  void operator()() ASIO_LVALUE_REF_QUAL ASIO_NOEXCEPT
+  {
+#if !defined(ASIO_NO_EXCEPTIONS)
+    try
+    {
+#endif // !defined(ASIO_NO_EXCEPTIONS)
+      execution::set_value(*receiver_);
+      ++(*ref_count_);
+    }
+#if !defined(ASIO_NO_EXCEPTIONS)
+    catch (...)
+    {
+#if defined(ASIO_HAS_STD_EXCEPTION_PTR)
+      execution::set_error(*receiver_,
+          std::make_exception_ptr(receiver_invocation_error()));
+      ++(*ref_count_);
+#else // defined(ASIO_HAS_STD_EXCEPTION_PTR)
+      std::terminate();
+#endif // defined(ASIO_HAS_STD_EXCEPTION_PTR)
+    }
+#endif // !defined(ASIO_NO_EXCEPTIONS)
+  }
+};
+
+#endif // defined(ASIO_HAS_MOVE)
+
+template <typename T>
+struct is_as_invocable : false_type
+{
+};
+
+template <typename Function, typename T>
+struct is_as_invocable<as_invocable<Function, T> > : true_type
+{
+};
+
+} // namespace detail
+} // namespace execution
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_EXECUTION_DETAIL_AS_INVOCABLE_HPP

extern/asio-1.18.2/include/asio/execution/detail/as_operation.hpp

@@ -0,0 +1,105 @@
+//
+// execution/detail/as_operation.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2021 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_EXECUTION_DETAIL_AS_OPERATION_HPP
+#define ASIO_EXECUTION_DETAIL_AS_OPERATION_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/detail/memory.hpp"
+#include "asio/detail/type_traits.hpp"
+#include "asio/execution/detail/as_invocable.hpp"
+#include "asio/execution/execute.hpp"
+#include "asio/execution/set_error.hpp"
+#include "asio/traits/start_member.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace execution {
+namespace detail {
+
+template <typename Executor, typename Receiver>
+struct as_operation
+{
+  typename remove_cvref<Executor>::type ex_;
+  typename remove_cvref<Receiver>::type receiver_;
+#if !defined(ASIO_HAS_MOVE)
+  asio::detail::shared_ptr<asio::detail::atomic_count> ref_count_;
+#endif // !defined(ASIO_HAS_MOVE)
+
+  template <typename E, typename R>
+  explicit as_operation(ASIO_MOVE_ARG(E) e, ASIO_MOVE_ARG(R) r)
+    : ex_(ASIO_MOVE_CAST(E)(e)),
+      receiver_(ASIO_MOVE_CAST(R)(r))
+#if !defined(ASIO_HAS_MOVE)
+      , ref_count_(new asio::detail::atomic_count(1))
+#endif // !defined(ASIO_HAS_MOVE)
+  {
+  }
+
+  void start() ASIO_NOEXCEPT
+  {
+#if !defined(ASIO_NO_EXCEPTIONS)
+    try
+    {
+#endif // !defined(ASIO_NO_EXCEPTIONS)
+      execution::execute(
+          ASIO_MOVE_CAST(typename remove_cvref<Executor>::type)(ex_),
+          as_invocable<typename remove_cvref<Receiver>::type,
+              Executor>(receiver_
+#if !defined(ASIO_HAS_MOVE)
+                , ref_count_
+#endif // !defined(ASIO_HAS_MOVE)
+              ));
+#if !defined(ASIO_NO_EXCEPTIONS)
+    }
+    catch (...)
+    {
+#if defined(ASIO_HAS_STD_EXCEPTION_PTR)
+      execution::set_error(
+          ASIO_MOVE_OR_LVALUE(
+            typename remove_cvref<Receiver>::type)(
+              receiver_),
+          std::current_exception());
+#else // defined(ASIO_HAS_STD_EXCEPTION_PTR)
+      std::terminate();
+#endif // defined(ASIO_HAS_STD_EXCEPTION_PTR)
+    }
+#endif // !defined(ASIO_NO_EXCEPTIONS)
+  }
+};
+
+} // namespace detail
+} // namespace execution
+namespace traits {
+
+#if !defined(ASIO_HAS_DEDUCED_START_MEMBER_TRAIT)
+
+template <typename Executor, typename Receiver>
+struct start_member<
+    asio::execution::detail::as_operation<Executor, Receiver> >
+{
+  ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+  typedef void result_type;
+};
+
+#endif // !defined(ASIO_HAS_DEDUCED_START_MEMBER_TRAIT)
+
+} // namespace traits
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_EXECUTION_DETAIL_AS_OPERATION_HPP

extern/asio-1.18.2/include/asio/execution/detail/as_receiver.hpp

@@ -0,0 +1,128 @@
+//
+// execution/detail/as_receiver.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2021 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_EXECUTION_DETAIL_AS_RECEIVER_HPP
+#define ASIO_EXECUTION_DETAIL_AS_RECEIVER_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/detail/type_traits.hpp"
+#include "asio/traits/set_done_member.hpp"
+#include "asio/traits/set_error_member.hpp"
+#include "asio/traits/set_value_member.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace execution {
+namespace detail {
+
+template <typename Function, typename>
+struct as_receiver
+{
+  Function f_;
+
+  template <typename F>
+  explicit as_receiver(ASIO_MOVE_ARG(F) f, int)
+    : f_(ASIO_MOVE_CAST(F)(f))
+  {
+  }
+
+#if defined(ASIO_MSVC) && defined(ASIO_HAS_MOVE)
+  as_receiver(as_receiver&& other)
+    : f_(ASIO_MOVE_CAST(Function)(other.f_))
+  {
+  }
+#endif // defined(ASIO_MSVC) && defined(ASIO_HAS_MOVE)
+
+  void set_value()
+    ASIO_NOEXCEPT_IF(noexcept(declval<Function&>()()))
+  {
+    f_();
+  }
+
+  template <typename E>
+  void set_error(E) ASIO_NOEXCEPT
+  {
+    std::terminate();
+  }
+
+  void set_done() ASIO_NOEXCEPT
+  {
+  }
+};
+
+template <typename T>
+struct is_as_receiver : false_type
+{
+};
+
+template <typename Function, typename T>
+struct is_as_receiver<as_receiver<Function, T> > : true_type
+{
+};
+
+} // namespace detail
+} // namespace execution
+namespace traits {
+
+#if !defined(ASIO_HAS_DEDUCED_SET_VALUE_MEMBER_TRAIT)
+
+template <typename Function, typename T>
+struct set_value_member<
+    asio::execution::detail::as_receiver<Function, T>, void()>
+{
+  ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+#if defined(ASIO_HAS_NOEXCEPT)
+  ASIO_STATIC_CONSTEXPR(bool,
+      is_noexcept = noexcept(declval<Function&>()()));
+#else // defined(ASIO_HAS_NOEXCEPT)
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+#endif // defined(ASIO_HAS_NOEXCEPT)
+  typedef void result_type;
+};
+
+#endif // !defined(ASIO_HAS_DEDUCED_SET_VALUE_MEMBER_TRAIT)
+
+#if !defined(ASIO_HAS_DEDUCED_SET_ERROR_MEMBER_TRAIT)
+
+template <typename Function, typename T, typename E>
+struct set_error_member<
+    asio::execution::detail::as_receiver<Function, T>, E>
+{
+  ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+  typedef void result_type;
+};
+
+#endif // !defined(ASIO_HAS_DEDUCED_SET_ERROR_MEMBER_TRAIT)
+
+#if !defined(ASIO_HAS_DEDUCED_SET_DONE_MEMBER_TRAIT)
+
+template <typename Function, typename T>
+struct set_done_member<
+    asio::execution::detail::as_receiver<Function, T> >
+{
+  ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+  typedef void result_type;
+};
+
+#endif // !defined(ASIO_HAS_DEDUCED_SET_DONE_MEMBER_TRAIT)
+
+} // namespace traits
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_EXECUTION_DETAIL_AS_RECEIVER_HPP

extern/asio-1.18.2/include/asio/execution/detail/bulk_sender.hpp

@@ -0,0 +1,261 @@
+//
+// execution/detail/bulk_sender.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2021 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_EXECUTION_DETAIL_BULK_SENDER_HPP
+#define ASIO_EXECUTION_DETAIL_BULK_SENDER_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/detail/type_traits.hpp"
+#include "asio/execution/connect.hpp"
+#include "asio/execution/executor.hpp"
+#include "asio/execution/set_done.hpp"
+#include "asio/execution/set_error.hpp"
+#include "asio/traits/connect_member.hpp"
+#include "asio/traits/set_done_member.hpp"
+#include "asio/traits/set_error_member.hpp"
+#include "asio/traits/set_value_member.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace execution {
+namespace detail {
+
+template <typename Receiver, typename Function, typename Number, typename Index>
+struct bulk_receiver
+{
+  typename remove_cvref<Receiver>::type receiver_;
+  typename decay<Function>::type f_;
+  typename decay<Number>::type n_;
+
+  template <typename R, typename F, typename N>
+  explicit bulk_receiver(ASIO_MOVE_ARG(R) r,
+      ASIO_MOVE_ARG(F) f, ASIO_MOVE_ARG(N) n)
+    : receiver_(ASIO_MOVE_CAST(R)(r)),
+      f_(ASIO_MOVE_CAST(F)(f)),
+      n_(ASIO_MOVE_CAST(N)(n))
+  {
+  }
+
+  void set_value()
+  {
+    for (Index i = 0; i < n_; ++i)
+      f_(i);
+
+    execution::set_value(
+        ASIO_MOVE_OR_LVALUE(
+          typename remove_cvref<Receiver>::type)(receiver_));
+  }
+
+  template <typename Error>
+  void set_error(ASIO_MOVE_ARG(Error) e) ASIO_NOEXCEPT
+  {
+    execution::set_error(
+        ASIO_MOVE_OR_LVALUE(
+          typename remove_cvref<Receiver>::type)(receiver_),
+        ASIO_MOVE_CAST(Error)(e));
+  }
+
+  void set_done() ASIO_NOEXCEPT
+  {
+    execution::set_done(
+        ASIO_MOVE_OR_LVALUE(
+          typename remove_cvref<Receiver>::type)(receiver_));
+  }
+};
+
+template <typename Sender, typename Receiver,
+  typename Function, typename Number>
+struct bulk_receiver_traits
+{
+  typedef bulk_receiver<
+      Receiver, Function, Number,
+      typename execution::executor_index<
+        typename remove_cvref<Sender>::type
+      >::type
+    > type;
+
+#if defined(ASIO_HAS_MOVE)
+  typedef type arg_type;
+#else // defined(ASIO_HAS_MOVE)
+  typedef const type& arg_type;
+#endif // defined(ASIO_HAS_MOVE)
+};
+
+template <typename Sender, typename Function, typename Number>
+struct bulk_sender : sender_base
+{
+  typename remove_cvref<Sender>::type sender_;
+  typename decay<Function>::type f_;
+  typename decay<Number>::type n_;
+
+  template <typename S, typename F, typename N>
+  explicit bulk_sender(ASIO_MOVE_ARG(S) s,
+      ASIO_MOVE_ARG(F) f, ASIO_MOVE_ARG(N) n)
+    : sender_(ASIO_MOVE_CAST(S)(s)),
+      f_(ASIO_MOVE_CAST(F)(f)),
+      n_(ASIO_MOVE_CAST(N)(n))
+  {
+  }
+
+  template <typename Receiver>
+  typename connect_result<
+      ASIO_MOVE_OR_LVALUE_TYPE(typename remove_cvref<Sender>::type),
+      typename bulk_receiver_traits<
+        Sender, Receiver, Function, Number
+      >::arg_type
+  >::type connect(ASIO_MOVE_ARG(Receiver) r,
+      typename enable_if<
+        can_connect<
+          typename remove_cvref<Sender>::type,
+          typename bulk_receiver_traits<
+            Sender, Receiver, Function, Number
+          >::arg_type
+        >::value
+      >::type* = 0) ASIO_RVALUE_REF_QUAL ASIO_NOEXCEPT
+  {
+    return execution::connect(
+        ASIO_MOVE_OR_LVALUE(typename remove_cvref<Sender>::type)(sender_),
+        typename bulk_receiver_traits<Sender, Receiver, Function, Number>::type(
+          ASIO_MOVE_CAST(Receiver)(r),
+          ASIO_MOVE_CAST(typename decay<Function>::type)(f_),
+          ASIO_MOVE_CAST(typename decay<Number>::type)(n_)));
+  }
+
+  template <typename Receiver>
+  typename connect_result<
+      const typename remove_cvref<Sender>::type&,
+      typename bulk_receiver_traits<
+        Sender, Receiver, Function, Number
+      >::arg_type
+  >::type connect(ASIO_MOVE_ARG(Receiver) r,
+      typename enable_if<
+        can_connect<
+          const typename remove_cvref<Sender>::type&,
+          typename bulk_receiver_traits<
+            Sender, Receiver, Function, Number
+          >::arg_type
+        >::value
+      >::type* = 0) const ASIO_LVALUE_REF_QUAL ASIO_NOEXCEPT
+  {
+    return execution::connect(sender_,
+        typename bulk_receiver_traits<Sender, Receiver, Function, Number>::type(
+          ASIO_MOVE_CAST(Receiver)(r), f_, n_));
+  }
+};
+
+} // namespace detail
+} // namespace execution
+namespace traits {
+
+#if !defined(ASIO_HAS_DEDUCED_SET_VALUE_MEMBER_TRAIT)
+
+template <typename Receiver, typename Function, typename Number, typename Index>
+struct set_value_member<
+    execution::detail::bulk_receiver<Receiver, Function, Number, Index>,
+    void()>
+{
+  ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef void result_type;
+};
+
+#endif // !defined(ASIO_HAS_DEDUCED_SET_VALUE_MEMBER_TRAIT)
+
+#if !defined(ASIO_HAS_DEDUCED_SET_ERROR_MEMBER_TRAIT)
+
+template <typename Receiver, typename Function,
+    typename Number, typename Index, typename Error>
+struct set_error_member<
+    execution::detail::bulk_receiver<Receiver, Function, Number, Index>,
+    Error>
+{
+  ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+  typedef void result_type;
+};
+
+#endif // !defined(ASIO_HAS_DEDUCED_SET_ERROR_MEMBER_TRAIT)
+
+#if !defined(ASIO_HAS_DEDUCED_SET_DONE_MEMBER_TRAIT)
+
+template <typename Receiver, typename Function, typename Number, typename Index>
+struct set_done_member<
+    execution::detail::bulk_receiver<Receiver, Function, Number, Index> >
+{
+  ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+  typedef void result_type;
+};
+
+#endif // !defined(ASIO_HAS_DEDUCED_SET_DONE_MEMBER_TRAIT)
+
+#if !defined(ASIO_HAS_DEDUCED_CONNECT_MEMBER_TRAIT)
+
+template <typename Sender, typename Function,
+    typename Number, typename Receiver>
+struct connect_member<
+    execution::detail::bulk_sender<Sender, Function, Number>,
+    Receiver,
+    typename enable_if<
+      execution::can_connect<
+        ASIO_MOVE_OR_LVALUE_TYPE(typename remove_cvref<Sender>::type),
+        typename execution::detail::bulk_receiver_traits<
+          Sender, Receiver, Function, Number
+        >::arg_type
+      >::value
+    >::type>
+{
+  ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef typename execution::connect_result<
+      ASIO_MOVE_OR_LVALUE_TYPE(typename remove_cvref<Sender>::type),
+      typename execution::detail::bulk_receiver_traits<
+        Sender, Receiver, Function, Number
+      >::arg_type
+    >::type result_type;
+};
+
+template <typename Sender, typename Function,
+    typename Number, typename Receiver>
+struct connect_member<
+    const execution::detail::bulk_sender<Sender, Function, Number>,
+    Receiver,
+    typename enable_if<
+      execution::can_connect<
+        const typename remove_cvref<Sender>::type&,
+        typename execution::detail::bulk_receiver_traits<
+          Sender, Receiver, Function, Number
+        >::arg_type
+      >::value
+    >::type>
+{
+  ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef typename execution::connect_result<
+      const typename remove_cvref<Sender>::type&,
+      typename execution::detail::bulk_receiver_traits<
+        Sender, Receiver, Function, Number
+      >::arg_type
+    >::type result_type;
+};
+
+#endif // !defined(ASIO_HAS_DEDUCED_CONNECT_MEMBER_TRAIT)
+
+} // namespace traits
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_EXECUTION_DETAIL_BULK_SENDER_HPP

extern/asio-1.18.2/include/asio/execution/detail/submit_receiver.hpp

@@ -0,0 +1,233 @@
+//
+// execution/detail/submit_receiver.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2021 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_EXECUTION_DETAIL_SUBMIT_RECEIVER_HPP
+#define ASIO_EXECUTION_DETAIL_SUBMIT_RECEIVER_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/detail/type_traits.hpp"
+#include "asio/detail/variadic_templates.hpp"
+#include "asio/execution/connect.hpp"
+#include "asio/execution/receiver.hpp"
+#include "asio/execution/set_done.hpp"
+#include "asio/execution/set_error.hpp"
+#include "asio/execution/set_value.hpp"
+#include "asio/traits/set_done_member.hpp"
+#include "asio/traits/set_error_member.hpp"
+#include "asio/traits/set_value_member.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace execution {
+namespace detail {
+
+template <typename Sender, typename Receiver>
+struct submit_receiver;
+
+template <typename Sender, typename Receiver>
+struct submit_receiver_wrapper
+{
+  submit_receiver<Sender, Receiver>* p_;
+
+  explicit submit_receiver_wrapper(submit_receiver<Sender, Receiver>* p)
+    : p_(p)
+  {
+  }
+
+#if defined(ASIO_HAS_VARIADIC_TEMPLATES)
+
+  template <typename... Args>
+  typename enable_if<is_receiver_of<Receiver, Args...>::value>::type
+  set_value(ASIO_MOVE_ARG(Args)... args) ASIO_RVALUE_REF_QUAL
+    ASIO_NOEXCEPT_IF((is_nothrow_receiver_of<Receiver, Args...>::value))
+  {
+    execution::set_value(
+        ASIO_MOVE_OR_LVALUE(
+          typename remove_cvref<Receiver>::type)(p_->r_),
+        ASIO_MOVE_CAST(Args)(args)...);
+    delete p_;
+  }
+
+#else // defined(ASIO_HAS_VARIADIC_TEMPLATES)
+
+  void set_value() ASIO_RVALUE_REF_QUAL
+    ASIO_NOEXCEPT_IF((is_nothrow_receiver_of<Receiver>::value))
+  {
+    execution::set_value(
+        ASIO_MOVE_OR_LVALUE(
+          typename remove_cvref<Receiver>::type)(p_->r_));
+    delete p_;
+  }
+
+#define ASIO_PRIVATE_SUBMIT_RECEIVER_SET_VALUE_DEF(n) \
+  template <ASIO_VARIADIC_TPARAMS(n)> \
+  typename enable_if<is_receiver_of<Receiver, \
+    ASIO_VARIADIC_TARGS(n)>::value>::type \
+  set_value(ASIO_VARIADIC_MOVE_PARAMS(n)) ASIO_RVALUE_REF_QUAL \
+    ASIO_NOEXCEPT_IF((is_nothrow_receiver_of< \
+      Receiver, ASIO_VARIADIC_TARGS(n)>::value)) \
+  { \
+    execution::set_value( \
+        ASIO_MOVE_OR_LVALUE( \
+          typename remove_cvref<Receiver>::type)(p_->r_), \
+        ASIO_VARIADIC_MOVE_ARGS(n)); \
+    delete p_; \
+  } \
+  /**/
+ASIO_VARIADIC_GENERATE(ASIO_PRIVATE_SUBMIT_RECEIVER_SET_VALUE_DEF)
+#undef ASIO_PRIVATE_SUBMIT_RECEIVER_SET_VALUE_DEF
+
+#endif // defined(ASIO_HAS_VARIADIC_TEMPLATES)
+
+  template <typename E>
+  void set_error(ASIO_MOVE_ARG(E) e)
+    ASIO_RVALUE_REF_QUAL ASIO_NOEXCEPT
+  {
+    execution::set_error(
+        ASIO_MOVE_OR_LVALUE(
+          typename remove_cvref<Receiver>::type)(p_->r_),
+        ASIO_MOVE_CAST(E)(e));
+    delete p_;
+  }
+
+  void set_done() ASIO_RVALUE_REF_QUAL ASIO_NOEXCEPT
+  {
+    execution::set_done(
+        ASIO_MOVE_OR_LVALUE(
+          typename remove_cvref<Receiver>::type)(p_->r_));
+    delete p_;
+  }
+};
+
+template <typename Sender, typename Receiver>
+struct submit_receiver
+{
+  typename remove_cvref<Receiver>::type r_;
+#if defined(ASIO_HAS_MOVE)
+  typename connect_result<Sender,
+      submit_receiver_wrapper<Sender, Receiver> >::type state_;
+#else // defined(ASIO_HAS_MOVE)
+  typename connect_result<Sender,
+      const submit_receiver_wrapper<Sender, Receiver>& >::type state_;
+#endif // defined(ASIO_HAS_MOVE)
+
+#if defined(ASIO_HAS_MOVE)
+  template <typename S, typename R>
+  explicit submit_receiver(ASIO_MOVE_ARG(S) s, ASIO_MOVE_ARG(R) r)
+    : r_(ASIO_MOVE_CAST(R)(r)),
+      state_(execution::connect(ASIO_MOVE_CAST(S)(s),
+            submit_receiver_wrapper<Sender, Receiver>(this)))
+  {
+  }
+#else // defined(ASIO_HAS_MOVE)
+  explicit submit_receiver(Sender s, Receiver r)
+    : r_(r),
+      state_(execution::connect(s,
+            submit_receiver_wrapper<Sender, Receiver>(this)))
+  {
+  }
+#endif // defined(ASIO_HAS_MOVE)
+};
+
+} // namespace detail
+} // namespace execution
+namespace traits {
+
+#if !defined(ASIO_HAS_DEDUCED_SET_VALUE_MEMBER_TRAIT)
+
+#if defined(ASIO_HAS_VARIADIC_TEMPLATES)
+
+template <typename Sender, typename Receiver, typename... Args>
+struct set_value_member<
+    asio::execution::detail::submit_receiver_wrapper<
+      Sender, Receiver>,
+    void(Args...)>
+{
+  ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept =
+    (asio::execution::is_nothrow_receiver_of<Receiver, Args...>::value));
+  typedef void result_type;
+};
+
+#else // defined(ASIO_HAS_VARIADIC_TEMPLATES)
+
+template <typename Sender, typename Receiver>
+struct set_value_member<
+    asio::execution::detail::submit_receiver_wrapper<
+      Sender, Receiver>,
+    void()>
+{
+  ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept =
+    asio::execution::is_nothrow_receiver_of<Receiver>::value);
+  typedef void result_type;
+};
+
+#define ASIO_PRIVATE_SUBMIT_RECEIVER_TRAIT_DEF(n) \
+  template <typename Sender, typename Receiver, \
+      ASIO_VARIADIC_TPARAMS(n)> \
+  struct set_value_member< \
+      asio::execution::detail::submit_receiver_wrapper< \
+        Sender, Receiver>, \
+      void(ASIO_VARIADIC_TARGS(n))> \
+  { \
+    ASIO_STATIC_CONSTEXPR(bool, is_valid = true); \
+    ASIO_STATIC_CONSTEXPR(bool, is_noexcept = \
+      (asio::execution::is_nothrow_receiver_of<Receiver, \
+        ASIO_VARIADIC_TARGS(n)>::value)); \
+    typedef void result_type; \
+  }; \
+  /**/
+ASIO_VARIADIC_GENERATE(ASIO_PRIVATE_SUBMIT_RECEIVER_TRAIT_DEF)
+#undef ASIO_PRIVATE_SUBMIT_RECEIVER_TRAIT_DEF
+
+#endif // defined(ASIO_HAS_VARIADIC_TEMPLATES)
+
+#endif // !defined(ASIO_HAS_DEDUCED_SET_VALUE_MEMBER_TRAIT)
+
+#if !defined(ASIO_HAS_DEDUCED_SET_ERROR_MEMBER_TRAIT)
+
+template <typename Sender, typename Receiver, typename E>
+struct set_error_member<
+    asio::execution::detail::submit_receiver_wrapper<
+      Sender, Receiver>, E>
+{
+  ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+  typedef void result_type;
+};
+
+#endif // !defined(ASIO_HAS_DEDUCED_SET_ERROR_MEMBER_TRAIT)
+
+#if !defined(ASIO_HAS_DEDUCED_SET_DONE_MEMBER_TRAIT)
+
+template <typename Sender, typename Receiver>
+struct set_done_member<
+    asio::execution::detail::submit_receiver_wrapper<
+      Sender, Receiver> >
+{
+  ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+  typedef void result_type;
+};
+
+#endif // !defined(ASIO_HAS_DEDUCED_SET_DONE_MEMBER_TRAIT)
+
+} // namespace traits
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_EXECUTION_DETAIL_SUBMIT_RECEIVER_HPP

extern/asio-1.18.2/include/asio/execution/detail/void_receiver.hpp

@@ -0,0 +1,90 @@
+//
+// execution/detail/void_receiver.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2021 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_EXECUTION_DETAIL_VOID_RECEIVER_HPP
+#define ASIO_EXECUTION_DETAIL_VOID_RECEIVER_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/traits/set_done_member.hpp"
+#include "asio/traits/set_error_member.hpp"
+#include "asio/traits/set_value_member.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace execution {
+namespace detail {
+
+struct void_receiver
+{
+  void set_value() ASIO_NOEXCEPT
+  {
+  }
+
+  template <typename E>
+  void set_error(ASIO_MOVE_ARG(E)) ASIO_NOEXCEPT
+  {
+  }
+
+  void set_done() ASIO_NOEXCEPT
+  {
+  }
+};
+
+} // namespace detail
+} // namespace execution
+namespace traits {
+
+#if !defined(ASIO_HAS_DEDUCED_SET_VALUE_MEMBER_TRAIT)
+
+template <>
+struct set_value_member<asio::execution::detail::void_receiver, void()>
+{
+  ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+  typedef void result_type;
+};
+
+#endif // !defined(ASIO_HAS_DEDUCED_SET_VALUE_MEMBER_TRAIT)
+
+#if !defined(ASIO_HAS_DEDUCED_SET_ERROR_MEMBER_TRAIT)
+
+template <typename E>
+struct set_error_member<asio::execution::detail::void_receiver, E>
+{
+  ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+  typedef void result_type;
+};
+
+#endif // !defined(ASIO_HAS_DEDUCED_SET_ERROR_MEMBER_TRAIT)
+
+#if !defined(ASIO_HAS_DEDUCED_SET_DONE_MEMBER_TRAIT)
+
+template <>
+struct set_done_member<asio::execution::detail::void_receiver>
+{
+  ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+  typedef void result_type;
+};
+
+#endif // !defined(ASIO_HAS_DEDUCED_SET_DONE_MEMBER_TRAIT)
+
+} // namespace traits
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_EXECUTION_DETAIL_VOID_RECEIVER_HPP

extern/asio-1.18.2/include/asio/execution/execute.hpp

@@ -0,0 +1,283 @@
+//
+// execution/execute.hpp
+// ~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2021 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_EXECUTION_EXECUTE_HPP
+#define ASIO_EXECUTION_EXECUTE_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/detail/type_traits.hpp"
+#include "asio/execution/detail/as_invocable.hpp"
+#include "asio/execution/detail/as_receiver.hpp"
+#include "asio/traits/execute_member.hpp"
+#include "asio/traits/execute_free.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+#if defined(GENERATING_DOCUMENTATION)
+
+namespace asio {
+namespace execution {
+
+/// A customisation point that executes a function on an executor.
+/**
+ * The name <tt>execution::execute</tt> denotes a customisation point object.
+ *
+ * For some subexpressions <tt>e</tt> and <tt>f</tt>, let <tt>E</tt> be a type
+ * such that <tt>decltype((e))</tt> is <tt>E</tt> and let <tt>F</tt> be a type
+ * such that <tt>decltype((f))</tt> is <tt>F</tt>. The expression
+ * <tt>execution::execute(e, f)</tt> is ill-formed if <tt>F</tt> does not model
+ * <tt>invocable</tt>, or if <tt>E</tt> does not model either <tt>executor</tt>
+ * or <tt>sender</tt>. Otherwise, it is expression-equivalent to:
+ *
+ * @li <tt>e.execute(f)</tt>, if that expression is valid. If the function
+ *   selected does not execute the function object <tt>f</tt> on the executor
+ *   <tt>e</tt>, the program is ill-formed with no diagnostic required.
+ *
+ * @li Otherwise, <tt>execute(e, f)</tt>, if that expression is valid, with
+ *   overload resolution performed in a context that includes the declaration
+ *   <tt>void execute();</tt> and that does not include a declaration of
+ *   <tt>execution::execute</tt>. If the function selected by overload
+ *   resolution does not execute the function object <tt>f</tt> on the executor
+ *   <tt>e</tt>, the program is ill-formed with no diagnostic required.
+ */
+inline constexpr unspecified execute = unspecified;
+
+/// A type trait that determines whether a @c execute expression is well-formed.
+/**
+ * Class template @c can_execute is a trait that is derived from
+ * @c true_type if the expression <tt>execution::execute(std::declval<T>(),
+ * std::declval<F>())</tt> is well formed; otherwise @c false_type.
+ */
+template <typename T, typename F>
+struct can_execute :
+  integral_constant<bool, automatically_determined>
+{
+};
+
+} // namespace execution
+} // namespace asio
+
+#else // defined(GENERATING_DOCUMENTATION)
+
+namespace asio {
+namespace execution {
+
+template <typename T, typename R>
+struct is_sender_to;
+
+namespace detail {
+
+template <typename S, typename R>
+void submit_helper(ASIO_MOVE_ARG(S) s, ASIO_MOVE_ARG(R) r);
+
+} // namespace detail
+} // namespace execution
+} // namespace asio
+namespace asio_execution_execute_fn {
+
+using asio::conditional;
+using asio::decay;
+using asio::declval;
+using asio::enable_if;
+using asio::execution::detail::as_receiver;
+using asio::execution::detail::is_as_invocable;
+using asio::execution::is_sender_to;
+using asio::false_type;
+using asio::result_of;
+using asio::traits::execute_free;
+using asio::traits::execute_member;
+using asio::true_type;
+using asio::void_type;
+
+void execute();
+
+enum overload_type
+{
+  call_member,
+  call_free,
+  adapter,
+  ill_formed
+};
+
+template <typename Impl, typename T, typename F, typename = void,
+    typename = void, typename = void, typename = void, typename = void>
+struct call_traits
+{
+  ASIO_STATIC_CONSTEXPR(overload_type, overload = ill_formed);
+};
+
+template <typename Impl, typename T, typename F>
+struct call_traits<Impl, T, void(F),
+  typename enable_if<
+    execute_member<typename Impl::template proxy<T>::type, F>::is_valid
+  >::type> :
+  execute_member<typename Impl::template proxy<T>::type, F>
+{
+  ASIO_STATIC_CONSTEXPR(overload_type, overload = call_member);
+};
+
+template <typename Impl, typename T, typename F>
+struct call_traits<Impl, T, void(F),
+  typename enable_if<
+    !execute_member<typename Impl::template proxy<T>, F>::is_valid
+  >::type,
+  typename enable_if<
+    execute_free<T, F>::is_valid
+  >::type> :
+  execute_free<T, F>
+{
+  ASIO_STATIC_CONSTEXPR(overload_type, overload = call_free);
+};
+
+template <typename Impl, typename T, typename F>
+struct call_traits<Impl, T, void(F),
+  typename enable_if<
+    !execute_member<typename Impl::template proxy<T>::type, F>::is_valid
+  >::type,
+  typename enable_if<
+    !execute_free<T, F>::is_valid
+  >::type,
+  typename void_type<
+   typename result_of<typename decay<F>::type&()>::type
+  >::type,
+  typename enable_if<
+    !is_as_invocable<typename decay<F>::type>::value
+  >::type,
+  typename enable_if<
+    is_sender_to<T, as_receiver<typename decay<F>::type, T> >::value
+  >::type>
+{
+  ASIO_STATIC_CONSTEXPR(overload_type, overload = adapter);
+  ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef void result_type;
+};
+
+struct impl
+{
+  template <typename T>
+  struct proxy
+  {
+#if defined(ASIO_HAS_DEDUCED_EXECUTE_MEMBER_TRAIT)
+    struct type
+    {
+      template <typename F>
+      auto execute(ASIO_MOVE_ARG(F) f)
+        noexcept(
+          noexcept(
+            declval<typename conditional<true, T, F>::type>().execute(
+              ASIO_MOVE_CAST(F)(f))
+          )
+        )
+        -> decltype(
+          declval<typename conditional<true, T, F>::type>().execute(
+            ASIO_MOVE_CAST(F)(f))
+        );
+    };
+#else // defined(ASIO_HAS_DEDUCED_EXECUTE_MEMBER_TRAIT)
+    typedef T type;
+#endif // defined(ASIO_HAS_DEDUCED_EXECUTE_MEMBER_TRAIT)
+  };
+
+  template <typename T, typename F>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<impl, T, void(F)>::overload == call_member,
+    typename call_traits<impl, T, void(F)>::result_type
+  >::type
+  operator()(
+      ASIO_MOVE_ARG(T) t,
+      ASIO_MOVE_ARG(F) f) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<impl, T, void(F)>::is_noexcept))
+  {
+    return ASIO_MOVE_CAST(T)(t).execute(ASIO_MOVE_CAST(F)(f));
+  }
+
+  template <typename T, typename F>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<impl, T, void(F)>::overload == call_free,
+    typename call_traits<impl, T, void(F)>::result_type
+  >::type
+  operator()(
+      ASIO_MOVE_ARG(T) t,
+      ASIO_MOVE_ARG(F) f) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<impl, T, void(F)>::is_noexcept))
+  {
+    return execute(ASIO_MOVE_CAST(T)(t), ASIO_MOVE_CAST(F)(f));
+  }
+
+  template <typename T, typename F>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<impl, T, void(F)>::overload == adapter,
+    typename call_traits<impl, T, void(F)>::result_type
+  >::type
+  operator()(
+      ASIO_MOVE_ARG(T) t,
+      ASIO_MOVE_ARG(F) f) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<impl, T, void(F)>::is_noexcept))
+  {
+    return asio::execution::detail::submit_helper(
+        ASIO_MOVE_CAST(T)(t),
+        as_receiver<typename decay<F>::type, T>(
+          ASIO_MOVE_CAST(F)(f), 0));
+  }
+};
+
+template <typename T = impl>
+struct static_instance
+{
+  static const T instance;
+};
+
+template <typename T>
+const T static_instance<T>::instance = {};
+
+} // namespace asio_execution_execute_fn
+namespace asio {
+namespace execution {
+namespace {
+
+static ASIO_CONSTEXPR const asio_execution_execute_fn::impl&
+  execute = asio_execution_execute_fn::static_instance<>::instance;
+
+} // namespace
+
+typedef asio_execution_execute_fn::impl execute_t;
+
+template <typename T, typename F>
+struct can_execute :
+  integral_constant<bool,
+    asio_execution_execute_fn::call_traits<
+      execute_t, T, void(F)>::overload !=
+        asio_execution_execute_fn::ill_formed>
+{
+};
+
+#if defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename T, typename F>
+constexpr bool can_execute_v = can_execute<T, F>::value;
+
+#endif // defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+} // namespace execution
+} // namespace asio
+
+#endif // defined(GENERATING_DOCUMENTATION)
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_EXECUTION_EXECUTE_HPP

extern/asio-1.18.2/include/asio/execution/executor.hpp

@@ -0,0 +1,252 @@
+//
+// execution/executor.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2021 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_EXECUTION_EXECUTOR_HPP
+#define ASIO_EXECUTION_EXECUTOR_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/detail/type_traits.hpp"
+#include "asio/execution/execute.hpp"
+#include "asio/execution/invocable_archetype.hpp"
+#include "asio/traits/equality_comparable.hpp"
+
+#if defined(ASIO_HAS_DEDUCED_EXECUTE_FREE_TRAIT) \
+  && defined(ASIO_HAS_DEDUCED_EXECUTE_MEMBER_TRAIT) \
+  && defined(ASIO_HAS_DEDUCED_EQUALITY_COMPARABLE_TRAIT)
+# define ASIO_HAS_DEDUCED_EXECUTION_IS_EXECUTOR_TRAIT 1
+#endif // defined(ASIO_HAS_DEDUCED_EXECUTE_FREE_TRAIT)
+       //   && defined(ASIO_HAS_DEDUCED_EXECUTE_MEMBER_TRAIT)
+       //   && defined(ASIO_HAS_DEDUCED_EQUALITY_COMPARABLE_TRAIT)
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace execution {
+namespace detail {
+
+template <typename T, typename F,
+    typename = void, typename = void, typename = void, typename = void,
+    typename = void, typename = void, typename = void, typename = void>
+struct is_executor_of_impl : false_type
+{
+};
+
+template <typename T, typename F>
+struct is_executor_of_impl<T, F,
+  typename enable_if<
+    can_execute<typename add_const<T>::type, F>::value
+  >::type,
+  typename void_type<
+    typename result_of<typename decay<F>::type&()>::type
+  >::type,
+  typename enable_if<
+    is_constructible<typename decay<F>::type, F>::value
+  >::type,
+  typename enable_if<
+    is_move_constructible<typename decay<F>::type>::value
+  >::type,
+#if defined(ASIO_HAS_NOEXCEPT)
+  typename enable_if<
+    is_nothrow_copy_constructible<T>::value
+  >::type,
+  typename enable_if<
+    is_nothrow_destructible<T>::value
+  >::type,
+#else // defined(ASIO_HAS_NOEXCEPT)
+  typename enable_if<
+    is_copy_constructible<T>::value
+  >::type,
+  typename enable_if<
+    is_destructible<T>::value
+  >::type,
+#endif // defined(ASIO_HAS_NOEXCEPT)
+  typename enable_if<
+    traits::equality_comparable<T>::is_valid
+  >::type,
+  typename enable_if<
+    traits::equality_comparable<T>::is_noexcept
+  >::type> : true_type
+{
+};
+
+template <typename T, typename = void>
+struct executor_shape
+{
+  typedef std::size_t type;
+};
+
+template <typename T>
+struct executor_shape<T,
+    typename void_type<
+      typename T::shape_type
+    >::type>
+{
+  typedef typename T::shape_type type;
+};
+
+template <typename T, typename Default, typename = void>
+struct executor_index
+{
+  typedef Default type;
+};
+
+template <typename T, typename Default>
+struct executor_index<T, Default,
+    typename void_type<
+      typename T::index_type
+    >::type>
+{
+  typedef typename T::index_type type;
+};
+
+} // namespace detail
+
+/// The is_executor trait detects whether a type T satisfies the
+/// execution::executor concept.
+/**
+ * Class template @c is_executor is a UnaryTypeTrait that is derived from @c
+ * true_type if the type @c T meets the concept definition for an executor,
+ * otherwise @c false_type.
+ */
+template <typename T>
+struct is_executor :
+#if defined(GENERATING_DOCUMENTATION)
+  integral_constant<bool, automatically_determined>
+#else // defined(GENERATING_DOCUMENTATION)
+  detail::is_executor_of_impl<T, invocable_archetype>
+#endif // defined(GENERATING_DOCUMENTATION)
+{
+};
+
+#if defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename T>
+ASIO_CONSTEXPR const bool is_executor_v = is_executor<T>::value;
+
+#endif // defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+#if defined(ASIO_HAS_CONCEPTS)
+
+template <typename T>
+ASIO_CONCEPT executor = is_executor<T>::value;
+
+#define ASIO_EXECUTION_EXECUTOR ::asio::execution::executor
+
+#else // defined(ASIO_HAS_CONCEPTS)
+
+#define ASIO_EXECUTION_EXECUTOR typename
+
+#endif // defined(ASIO_HAS_CONCEPTS)
+
+/// The is_executor_of trait detects whether a type T satisfies the
+/// execution::executor_of concept for some set of value arguments.
+/**
+ * Class template @c is_executor_of is a type trait that is derived from @c
+ * true_type if the type @c T meets the concept definition for an executor
+ * that is invocable with a function object of type @c F, otherwise @c
+ * false_type.
+ */
+template <typename T, typename F>
+struct is_executor_of :
+#if defined(GENERATING_DOCUMENTATION)
+  integral_constant<bool, automatically_determined>
+#else // defined(GENERATING_DOCUMENTATION)
+  integral_constant<bool,
+    is_executor<T>::value && detail::is_executor_of_impl<T, F>::value
+  >
+#endif // defined(GENERATING_DOCUMENTATION)
+{
+};
+
+#if defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename T, typename F>
+ASIO_CONSTEXPR const bool is_executor_of_v =
+  is_executor_of<T, F>::value;
+
+#endif // defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+#if defined(ASIO_HAS_CONCEPTS)
+
+template <typename T, typename F>
+ASIO_CONCEPT executor_of = is_executor_of<T, F>::value;
+
+#define ASIO_EXECUTION_EXECUTOR_OF(f) \
+  ::asio::execution::executor_of<f>
+
+#else // defined(ASIO_HAS_CONCEPTS)
+
+#define ASIO_EXECUTION_EXECUTOR_OF typename
+
+#endif // defined(ASIO_HAS_CONCEPTS)
+
+/// The executor_shape trait detects the type used by an executor to represent
+/// the shape of a bulk operation.
+/**
+ * Class template @c executor_shape is a type trait with a nested type alias
+ * @c type whose type is @c T::shape_type if @c T::shape_type is valid,
+ * otherwise @c std::size_t.
+ */
+template <typename T>
+struct executor_shape
+#if !defined(GENERATING_DOCUMENTATION)
+  : detail::executor_shape<T>
+#endif // !defined(GENERATING_DOCUMENTATION)
+{
+#if defined(GENERATING_DOCUMENTATION)
+ /// @c T::shape_type if @c T::shape_type is valid, otherwise @c std::size_t.
+ typedef automatically_determined type;
+#endif // defined(GENERATING_DOCUMENTATION)
+};
+
+#if defined(ASIO_HAS_ALIAS_TEMPLATES)
+
+template <typename T>
+using executor_shape_t = typename executor_shape<T>::type;
+
+#endif // defined(ASIO_HAS_ALIAS_TEMPLATES)
+
+/// The executor_index trait detects the type used by an executor to represent
+/// an index within a bulk operation.
+/**
+ * Class template @c executor_index is a type trait with a nested type alias
+ * @c type whose type is @c T::index_type if @c T::index_type is valid,
+ * otherwise @c executor_shape_t<T>.
+ */
+template <typename T>
+struct executor_index
+#if !defined(GENERATING_DOCUMENTATION)
+  : detail::executor_index<T, typename executor_shape<T>::type>
+#endif // !defined(GENERATING_DOCUMENTATION)
+{
+#if defined(GENERATING_DOCUMENTATION)
+ /// @c T::index_type if @c T::index_type is valid, otherwise
+ /// @c executor_shape_t<T>.
+ typedef automatically_determined type;
+#endif // defined(GENERATING_DOCUMENTATION)
+};
+
+#if defined(ASIO_HAS_ALIAS_TEMPLATES)
+
+template <typename T>
+using executor_index_t = typename executor_index<T>::type;
+
+#endif // defined(ASIO_HAS_ALIAS_TEMPLATES)
+
+} // namespace execution
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_EXECUTION_EXECUTOR_HPP

extern/asio-1.18.2/include/asio/execution/impl/bad_executor.ipp

@@ -0,0 +1,40 @@
+//
+// exection/impl/bad_executor.ipp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2021 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_EXECUTION_IMPL_BAD_EXECUTOR_IPP
+#define ASIO_EXECUTION_IMPL_BAD_EXECUTOR_IPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/execution/bad_executor.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace execution {
+
+bad_executor::bad_executor() ASIO_NOEXCEPT
+{
+}
+
+const char* bad_executor::what() const ASIO_NOEXCEPT_OR_NOTHROW
+{
+  return "bad executor";
+}
+
+} // namespace execution
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_EXECUTION_IMPL_BAD_EXECUTOR_IPP

extern/asio-1.18.2/include/asio/execution/impl/receiver_invocation_error.ipp

@@ -0,0 +1,36 @@
+//
+// exection/impl/receiver_invocation_error.ipp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2021 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_EXECUTION_IMPL_RECEIVER_INVOCATION_ERROR_IPP
+#define ASIO_EXECUTION_IMPL_RECEIVER_INVOCATION_ERROR_IPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/execution/receiver_invocation_error.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace execution {
+
+receiver_invocation_error::receiver_invocation_error()
+  : std::runtime_error("receiver invocation error")
+{
+}
+
+} // namespace execution
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_EXECUTION_IMPL_RECEIVER_INVOCATION_ERROR_IPP

extern/asio-1.18.2/include/asio/execution/invocable_archetype.hpp

@@ -0,0 +1,71 @@
+//
+// execution/invocable_archetype.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2021 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_EXECUTION_INVOCABLE_ARCHETYPE_HPP
+#define ASIO_EXECUTION_INVOCABLE_ARCHETYPE_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/detail/type_traits.hpp"
+#include "asio/detail/variadic_templates.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace execution {
+
+/// An archetypal function object used for determining adherence to the
+/// execution::executor concept.
+struct invocable_archetype
+{
+#if !defined(GENERATING_DOCUMENTATION)
+  // Necessary for compatibility with a C++03 implementation of result_of.
+  typedef void result_type;
+#endif // !defined(GENERATING_DOCUMENTATION)
+
+#if defined(ASIO_HAS_VARIADIC_TEMPLATES) \
+  || defined(GENERATING_DOCUMENTATION)
+
+  /// Function call operator.
+  template <typename... Args>
+  void operator()(ASIO_MOVE_ARG(Args)...)
+  {
+  }
+
+#else // defined(ASIO_HAS_VARIADIC_TEMPLATES)
+      //   || defined(GENERATING_DOCUMENTATION)
+
+  void operator()()
+  {
+  }
+
+#define ASIO_PRIVATE_INVOCABLE_ARCHETYPE_CALL_DEF(n) \
+  template <ASIO_VARIADIC_TPARAMS(n)> \
+  void operator()(ASIO_VARIADIC_UNNAMED_MOVE_PARAMS(n)) \
+  { \
+  } \
+  /**/
+  ASIO_VARIADIC_GENERATE(ASIO_PRIVATE_INVOCABLE_ARCHETYPE_CALL_DEF)
+#undef ASIO_PRIVATE_INVOCABLE_ARCHETYPE_CALL_DEF
+
+#endif // defined(ASIO_HAS_VARIADIC_TEMPLATES)
+       //   || defined(GENERATING_DOCUMENTATION)
+};
+
+} // namespace execution
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_EXECUTION_INVOCABLE_ARCHETYPE_HPP
+

extern/asio-1.18.2/include/asio/execution/occupancy.hpp

@@ -0,0 +1,226 @@
+//
+// execution/occupancy.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2021 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_EXECUTION_OCCUPANCY_HPP
+#define ASIO_EXECUTION_OCCUPANCY_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/detail/type_traits.hpp"
+#include "asio/execution/executor.hpp"
+#include "asio/execution/scheduler.hpp"
+#include "asio/execution/sender.hpp"
+#include "asio/is_applicable_property.hpp"
+#include "asio/traits/query_static_constexpr_member.hpp"
+#include "asio/traits/static_query.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+
+#if defined(GENERATING_DOCUMENTATION)
+
+namespace execution {
+
+/// A property that gives an estimate of the number of execution agents that
+/// should occupy the associated execution context.
+struct occupancy_t
+{
+  /// The occupancy_t property applies to executors, senders, and schedulers.
+  template <typename T>
+  static constexpr bool is_applicable_property_v =
+    is_executor_v<T> || is_sender_v<T> || is_scheduler_v<T>;
+
+  /// The occupancy_t property cannot be required.
+  static constexpr bool is_requirable = false;
+
+  /// The occupancy_t property cannot be preferred.
+  static constexpr bool is_preferable = false;
+
+  /// The type returned by queries against an @c any_executor.
+  typedef std::size_t polymorphic_query_result_type;
+};
+
+/// A special value used for accessing the occupancy_t property.
+constexpr occupancy_t occupancy;
+
+} // namespace execution
+
+#else // defined(GENERATING_DOCUMENTATION)
+
+namespace execution {
+namespace detail {
+
+template <int I = 0>
+struct occupancy_t
+{
+#if defined(ASIO_HAS_VARIABLE_TEMPLATES)
+  template <typename T>
+  ASIO_STATIC_CONSTEXPR(bool,
+    is_applicable_property_v = (
+      is_executor<T>::value
+        || conditional<
+            is_executor<T>::value,
+            false_type,
+            is_sender<T>
+          >::type::value
+        || conditional<
+            is_executor<T>::value,
+            false_type,
+            is_scheduler<T>
+          >::type::value));
+#endif // defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+  ASIO_STATIC_CONSTEXPR(bool, is_requirable = false);
+  ASIO_STATIC_CONSTEXPR(bool, is_preferable = false);
+  typedef std::size_t polymorphic_query_result_type;
+
+  ASIO_CONSTEXPR occupancy_t()
+  {
+  }
+
+  template <typename T>
+  struct static_proxy
+  {
+#if defined(ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
+    struct type
+    {
+      template <typename P>
+      static constexpr auto query(ASIO_MOVE_ARG(P) p)
+        noexcept(
+          noexcept(
+            conditional<true, T, P>::type::query(ASIO_MOVE_CAST(P)(p))
+          )
+        )
+        -> decltype(
+          conditional<true, T, P>::type::query(ASIO_MOVE_CAST(P)(p))
+        )
+      {
+        return T::query(ASIO_MOVE_CAST(P)(p));
+      }
+    };
+#else // defined(ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
+    typedef T type;
+#endif // defined(ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
+  };
+
+  template <typename T>
+  struct query_static_constexpr_member :
+    traits::query_static_constexpr_member<
+      typename static_proxy<T>::type, occupancy_t> {};
+
+#if defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+  template <typename T>
+  static ASIO_CONSTEXPR
+  typename query_static_constexpr_member<T>::result_type
+  static_query()
+    ASIO_NOEXCEPT_IF((
+      query_static_constexpr_member<T>::is_noexcept))
+  {
+    return query_static_constexpr_member<T>::value();
+  }
+
+  template <typename E, typename T = decltype(occupancy_t::static_query<E>())>
+  static ASIO_CONSTEXPR const T static_query_v
+    = occupancy_t::static_query<E>();
+#endif // defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+#if !defined(ASIO_HAS_CONSTEXPR)
+  static const occupancy_t instance;
+#endif // !defined(ASIO_HAS_CONSTEXPR)
+};
+
+#if defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+template <int I> template <typename E, typename T>
+const T occupancy_t<I>::static_query_v;
+#endif // defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+#if !defined(ASIO_HAS_CONSTEXPR)
+template <int I>
+const occupancy_t<I> occupancy_t<I>::instance;
+#endif
+
+} // namespace detail
+
+typedef detail::occupancy_t<> occupancy_t;
+
+#if defined(ASIO_HAS_CONSTEXPR) || defined(GENERATING_DOCUMENTATION)
+constexpr occupancy_t occupancy;
+#else // defined(ASIO_HAS_CONSTEXPR) || defined(GENERATING_DOCUMENTATION)
+namespace { static const occupancy_t& occupancy = occupancy_t::instance; }
+#endif
+
+} // namespace execution
+
+#if !defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename T>
+struct is_applicable_property<T, execution::occupancy_t>
+  : integral_constant<bool,
+      execution::is_executor<T>::value
+        || conditional<
+            execution::is_executor<T>::value,
+            false_type,
+            execution::is_sender<T>
+          >::type::value
+        || conditional<
+            execution::is_executor<T>::value,
+            false_type,
+            execution::is_scheduler<T>
+          >::type::value>
+{
+};
+
+#endif // !defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+namespace traits {
+
+#if !defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  || !defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+template <typename T>
+struct static_query<T, execution::occupancy_t,
+  typename enable_if<
+    execution::detail::occupancy_t<0>::
+      query_static_constexpr_member<T>::is_valid
+  >::type>
+{
+  ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename execution::detail::occupancy_t<0>::
+    query_static_constexpr_member<T>::result_type result_type;
+
+  static ASIO_CONSTEXPR result_type value()
+  {
+    return execution::detail::occupancy_t<0>::
+      query_static_constexpr_member<T>::value();
+  }
+};
+
+#endif // !defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   || !defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+} // namespace traits
+
+#endif // defined(GENERATING_DOCUMENTATION)
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_EXECUTION_OCCUPANCY_HPP

extern/asio-1.18.2/include/asio/execution/operation_state.hpp

@@ -0,0 +1,94 @@
+//
+// execution/operation_state.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2021 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_EXECUTION_OPERATION_STATE_HPP
+#define ASIO_EXECUTION_OPERATION_STATE_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/detail/type_traits.hpp"
+#include "asio/execution/start.hpp"
+
+#if defined(ASIO_HAS_DEDUCED_START_FREE_TRAIT) \
+  && defined(ASIO_HAS_DEDUCED_START_MEMBER_TRAIT)
+# define ASIO_HAS_DEDUCED_EXECUTION_IS_OPERATION_STATE_TRAIT 1
+#endif // defined(ASIO_HAS_DEDUCED_START_FREE_TRAIT)
+       //   && defined(ASIO_HAS_DEDUCED_START_MEMBER_TRAIT)
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace execution {
+namespace detail {
+
+template <typename T>
+struct is_operation_state_base :
+  integral_constant<bool,
+    is_destructible<T>::value
+      && is_object<T>::value
+  >
+{
+};
+
+} // namespace detail
+
+/// The is_operation_state trait detects whether a type T satisfies the
+/// execution::operation_state concept.
+/**
+ * Class template @c is_operation_state is a type trait that is derived from
+ * @c true_type if the type @c T meets the concept definition for an
+ * @c operation_state, otherwise @c false_type.
+ */
+template <typename T>
+struct is_operation_state :
+#if defined(GENERATING_DOCUMENTATION)
+  integral_constant<bool, automatically_determined>
+#else // defined(GENERATING_DOCUMENTATION)
+  conditional<
+    can_start<typename add_lvalue_reference<T>::type>::value
+      && is_nothrow_start<typename add_lvalue_reference<T>::type>::value,
+    detail::is_operation_state_base<T>,
+    false_type
+  >::type
+#endif // defined(GENERATING_DOCUMENTATION)
+{
+};
+
+#if defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename T>
+ASIO_CONSTEXPR const bool is_operation_state_v =
+  is_operation_state<T>::value;
+
+#endif // defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+#if defined(ASIO_HAS_CONCEPTS)
+
+template <typename T>
+ASIO_CONCEPT operation_state = is_operation_state<T>::value;
+
+#define ASIO_EXECUTION_OPERATION_STATE \
+  ::asio::execution::operation_state
+
+#else // defined(ASIO_HAS_CONCEPTS)
+
+#define ASIO_EXECUTION_OPERATION_STATE typename
+
+#endif // defined(ASIO_HAS_CONCEPTS)
+
+} // namespace execution
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_EXECUTION_OPERATION_STATE_HPP

extern/asio-1.18.2/include/asio/execution/outstanding_work.hpp

@@ -0,0 +1,867 @@
+//
+// execution/outstanding_work.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2021 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_EXECUTION_OUTSTANDING_WORK_HPP
+#define ASIO_EXECUTION_OUTSTANDING_WORK_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/detail/type_traits.hpp"
+#include "asio/execution/executor.hpp"
+#include "asio/execution/scheduler.hpp"
+#include "asio/execution/sender.hpp"
+#include "asio/is_applicable_property.hpp"
+#include "asio/query.hpp"
+#include "asio/traits/query_free.hpp"
+#include "asio/traits/query_member.hpp"
+#include "asio/traits/query_static_constexpr_member.hpp"
+#include "asio/traits/static_query.hpp"
+#include "asio/traits/static_require.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+
+#if defined(GENERATING_DOCUMENTATION)
+
+namespace execution {
+
+/// A property to describe whether task submission is likely in the future.
+struct outstanding_work_t
+{
+  /// The outstanding_work_t property applies to executors, senders, and
+  /// schedulers.
+  template <typename T>
+  static constexpr bool is_applicable_property_v =
+    is_executor_v<T> || is_sender_v<T> || is_scheduler_v<T>;
+
+  /// The top-level outstanding_work_t property cannot be required.
+  static constexpr bool is_requirable = false;
+
+  /// The top-level outstanding_work_t property cannot be preferred.
+  static constexpr bool is_preferable = false;
+
+  /// The type returned by queries against an @c any_executor.
+  typedef outstanding_work_t polymorphic_query_result_type;
+
+  /// A sub-property that indicates that the executor does not represent likely
+  /// future submission of a function object.
+  struct untracked_t
+  {
+    /// The outstanding_work_t::untracked_t property applies to executors,
+    /// senders, and schedulers.
+    template <typename T>
+    static constexpr bool is_applicable_property_v =
+      is_executor_v<T> || is_sender_v<T> || is_scheduler_v<T>;
+
+    /// The outstanding_work_t::untracked_t property can be required.
+    static constexpr bool is_requirable = true;
+
+    /// The outstanding_work_t::untracked_t property can be preferred.
+    static constexpr bool is_preferable = true;
+
+    /// The type returned by queries against an @c any_executor.
+    typedef outstanding_work_t polymorphic_query_result_type;
+
+    /// Default constructor.
+    constexpr untracked_t();
+
+    /// Get the value associated with a property object.
+    /**
+     * @returns untracked_t();
+     */
+    static constexpr outstanding_work_t value();
+  };
+
+  /// A sub-property that indicates that the executor represents likely
+  /// future submission of a function object.
+  struct tracked_t
+  {
+    /// The outstanding_work_t::untracked_t property applies to executors,
+    /// senders, and schedulers.
+    template <typename T>
+    static constexpr bool is_applicable_property_v =
+      is_executor_v<T> || is_sender_v<T> || is_scheduler_v<T>;
+
+    /// The outstanding_work_t::tracked_t property can be required.
+    static constexpr bool is_requirable = true;
+
+    /// The outstanding_work_t::tracked_t property can be preferred.
+    static constexpr bool is_preferable = true;
+
+    /// The type returned by queries against an @c any_executor.
+    typedef outstanding_work_t polymorphic_query_result_type;
+
+    /// Default constructor.
+    constexpr tracked_t();
+
+    /// Get the value associated with a property object.
+    /**
+     * @returns tracked_t();
+     */
+    static constexpr outstanding_work_t value();
+  };
+
+  /// A special value used for accessing the outstanding_work_t::untracked_t
+  /// property.
+  static constexpr untracked_t untracked;
+
+  /// A special value used for accessing the outstanding_work_t::tracked_t
+  /// property.
+  static constexpr tracked_t tracked;
+
+  /// Default constructor.
+  constexpr outstanding_work_t();
+
+  /// Construct from a sub-property value.
+  constexpr outstanding_work_t(untracked_t);
+
+  /// Construct from a sub-property value.
+  constexpr outstanding_work_t(tracked_t);
+
+  /// Compare property values for equality.
+  friend constexpr bool operator==(
+      const outstanding_work_t& a, const outstanding_work_t& b) noexcept;
+
+  /// Compare property values for inequality.
+  friend constexpr bool operator!=(
+      const outstanding_work_t& a, const outstanding_work_t& b) noexcept;
+};
+
+/// A special value used for accessing the outstanding_work_t property.
+constexpr outstanding_work_t outstanding_work;
+
+} // namespace execution
+
+#else // defined(GENERATING_DOCUMENTATION)
+
+namespace execution {
+namespace detail {
+namespace outstanding_work {
+
+template <int I> struct untracked_t;
+template <int I> struct tracked_t;
+
+} // namespace outstanding_work
+
+template <int I = 0>
+struct outstanding_work_t
+{
+#if defined(ASIO_HAS_VARIABLE_TEMPLATES)
+  template <typename T>
+  ASIO_STATIC_CONSTEXPR(bool,
+    is_applicable_property_v = (
+      is_executor<T>::value
+        || conditional<
+            is_executor<T>::value,
+            false_type,
+            is_sender<T>
+          >::type::value
+        || conditional<
+            is_executor<T>::value,
+            false_type,
+            is_scheduler<T>
+          >::type::value));
+#endif // defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+  ASIO_STATIC_CONSTEXPR(bool, is_requirable = false);
+  ASIO_STATIC_CONSTEXPR(bool, is_preferable = false);
+  typedef outstanding_work_t polymorphic_query_result_type;
+
+  typedef detail::outstanding_work::untracked_t<I> untracked_t;
+  typedef detail::outstanding_work::tracked_t<I> tracked_t;
+
+  ASIO_CONSTEXPR outstanding_work_t()
+    : value_(-1)
+  {
+  }
+
+  ASIO_CONSTEXPR outstanding_work_t(untracked_t)
+    : value_(0)
+  {
+  }
+
+  ASIO_CONSTEXPR outstanding_work_t(tracked_t)
+    : value_(1)
+  {
+  }
+
+  template <typename T>
+  struct proxy
+  {
+#if defined(ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
+    struct type
+    {
+      template <typename P>
+      auto query(ASIO_MOVE_ARG(P) p) const
+        noexcept(
+          noexcept(
+            declval<typename conditional<true, T, P>::type>().query(
+              ASIO_MOVE_CAST(P)(p))
+          )
+        )
+        -> decltype(
+          declval<typename conditional<true, T, P>::type>().query(
+            ASIO_MOVE_CAST(P)(p))
+        );
+    };
+#else // defined(ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
+    typedef T type;
+#endif // defined(ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
+  };
+
+  template <typename T>
+  struct static_proxy
+  {
+#if defined(ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
+    struct type
+    {
+      template <typename P>
+      static constexpr auto query(ASIO_MOVE_ARG(P) p)
+        noexcept(
+          noexcept(
+            conditional<true, T, P>::type::query(ASIO_MOVE_CAST(P)(p))
+          )
+        )
+        -> decltype(
+          conditional<true, T, P>::type::query(ASIO_MOVE_CAST(P)(p))
+        )
+      {
+        return T::query(ASIO_MOVE_CAST(P)(p));
+      }
+    };
+#else // defined(ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
+    typedef T type;
+#endif // defined(ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
+  };
+
+  template <typename T>
+  struct query_member :
+    traits::query_member<typename proxy<T>::type, outstanding_work_t> {};
+
+  template <typename T>
+  struct query_static_constexpr_member :
+    traits::query_static_constexpr_member<
+      typename static_proxy<T>::type, outstanding_work_t> {};
+
+#if defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+  template <typename T>
+  static ASIO_CONSTEXPR
+  typename query_static_constexpr_member<T>::result_type
+  static_query()
+    ASIO_NOEXCEPT_IF((
+      query_static_constexpr_member<T>::is_noexcept))
+  {
+    return query_static_constexpr_member<T>::value();
+  }
+
+  template <typename T>
+  static ASIO_CONSTEXPR
+  typename traits::static_query<T, untracked_t>::result_type
+  static_query(
+      typename enable_if<
+        !query_static_constexpr_member<T>::is_valid
+      >::type* = 0,
+      typename enable_if<
+        !query_member<T>::is_valid
+      >::type* = 0,
+      typename enable_if<
+        traits::static_query<T, untracked_t>::is_valid
+      >::type* = 0) ASIO_NOEXCEPT
+  {
+    return traits::static_query<T, untracked_t>::value();
+  }
+
+  template <typename T>
+  static ASIO_CONSTEXPR
+  typename traits::static_query<T, tracked_t>::result_type
+  static_query(
+      typename enable_if<
+        !query_static_constexpr_member<T>::is_valid
+      >::type* = 0,
+      typename enable_if<
+        !query_member<T>::is_valid
+      >::type* = 0,
+      typename enable_if<
+        !traits::static_query<T, untracked_t>::is_valid
+      >::type* = 0,
+      typename enable_if<
+        traits::static_query<T, tracked_t>::is_valid
+      >::type* = 0) ASIO_NOEXCEPT
+  {
+    return traits::static_query<T, tracked_t>::value();
+  }
+
+  template <typename E,
+      typename T = decltype(outstanding_work_t::static_query<E>())>
+  static ASIO_CONSTEXPR const T static_query_v
+    = outstanding_work_t::static_query<E>();
+#endif // defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+  friend ASIO_CONSTEXPR bool operator==(
+      const outstanding_work_t& a, const outstanding_work_t& b)
+  {
+    return a.value_ == b.value_;
+  }
+
+  friend ASIO_CONSTEXPR bool operator!=(
+      const outstanding_work_t& a, const outstanding_work_t& b)
+  {
+    return a.value_ != b.value_;
+  }
+
+  struct convertible_from_outstanding_work_t
+  {
+    ASIO_CONSTEXPR convertible_from_outstanding_work_t(outstanding_work_t)
+    {
+    }
+  };
+
+  template <typename Executor>
+  friend ASIO_CONSTEXPR outstanding_work_t query(
+      const Executor& ex, convertible_from_outstanding_work_t,
+      typename enable_if<
+        can_query<const Executor&, untracked_t>::value
+      >::type* = 0)
+#if !defined(__clang__) // Clang crashes if noexcept is used here.
+#if defined(ASIO_MSVC) // Visual C++ wants the type to be qualified.
+    ASIO_NOEXCEPT_IF((
+      is_nothrow_query<const Executor&,
+        outstanding_work_t<>::untracked_t>::value))
+#else // defined(ASIO_MSVC)
+    ASIO_NOEXCEPT_IF((
+      is_nothrow_query<const Executor&, untracked_t>::value))
+#endif // defined(ASIO_MSVC)
+#endif // !defined(__clang__)
+  {
+    return asio::query(ex, untracked_t());
+  }
+
+  template <typename Executor>
+  friend ASIO_CONSTEXPR outstanding_work_t query(
+      const Executor& ex, convertible_from_outstanding_work_t,
+      typename enable_if<
+        !can_query<const Executor&, untracked_t>::value
+      >::type* = 0,
+      typename enable_if<
+        can_query<const Executor&, tracked_t>::value
+      >::type* = 0)
+#if !defined(__clang__) // Clang crashes if noexcept is used here.
+#if defined(ASIO_MSVC) // Visual C++ wants the type to be qualified.
+    ASIO_NOEXCEPT_IF((
+      is_nothrow_query<const Executor&,
+        outstanding_work_t<>::tracked_t>::value))
+#else // defined(ASIO_MSVC)
+    ASIO_NOEXCEPT_IF((
+      is_nothrow_query<const Executor&, tracked_t>::value))
+#endif // defined(ASIO_MSVC)
+#endif // !defined(__clang__)
+  {
+    return asio::query(ex, tracked_t());
+  }
+
+  ASIO_STATIC_CONSTEXPR_DEFAULT_INIT(untracked_t, untracked);
+  ASIO_STATIC_CONSTEXPR_DEFAULT_INIT(tracked_t, tracked);
+
+#if !defined(ASIO_HAS_CONSTEXPR)
+  static const outstanding_work_t instance;
+#endif // !defined(ASIO_HAS_CONSTEXPR)
+
+private:
+  int value_;
+};
+
+#if defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+template <int I> template <typename E, typename T>
+const T outstanding_work_t<I>::static_query_v;
+#endif // defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+#if !defined(ASIO_HAS_CONSTEXPR)
+template <int I>
+const outstanding_work_t<I> outstanding_work_t<I>::instance;
+#endif
+
+template <int I>
+const typename outstanding_work_t<I>::untracked_t
+outstanding_work_t<I>::untracked;
+
+template <int I>
+const typename outstanding_work_t<I>::tracked_t
+outstanding_work_t<I>::tracked;
+
+namespace outstanding_work {
+
+template <int I = 0>
+struct untracked_t
+{
+#if defined(ASIO_HAS_VARIABLE_TEMPLATES)
+  template <typename T>
+  ASIO_STATIC_CONSTEXPR(bool,
+    is_applicable_property_v = (
+      is_executor<T>::value
+        || conditional<
+            is_executor<T>::value,
+            false_type,
+            is_sender<T>
+          >::type::value
+        || conditional<
+            is_executor<T>::value,
+            false_type,
+            is_scheduler<T>
+          >::type::value));
+#endif // defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+  ASIO_STATIC_CONSTEXPR(bool, is_requirable = true);
+  ASIO_STATIC_CONSTEXPR(bool, is_preferable = true);
+  typedef outstanding_work_t<I> polymorphic_query_result_type;
+
+  ASIO_CONSTEXPR untracked_t()
+  {
+  }
+
+  template <typename T>
+  struct query_member :
+    traits::query_member<
+      typename outstanding_work_t<I>::template proxy<T>::type, untracked_t> {};
+
+  template <typename T>
+  struct query_static_constexpr_member :
+    traits::query_static_constexpr_member<
+      typename outstanding_work_t<I>::template static_proxy<T>::type,
+        untracked_t> {};
+
+#if defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+  template <typename T>
+  static ASIO_CONSTEXPR
+  typename query_static_constexpr_member<T>::result_type
+  static_query()
+    ASIO_NOEXCEPT_IF((
+      query_static_constexpr_member<T>::is_noexcept))
+  {
+    return query_static_constexpr_member<T>::value();
+  }
+
+  template <typename T>
+  static ASIO_CONSTEXPR untracked_t static_query(
+      typename enable_if<
+        !query_static_constexpr_member<T>::is_valid
+      >::type* = 0,
+      typename enable_if<
+        !query_member<T>::is_valid
+      >::type* = 0,
+      typename enable_if<
+        !traits::query_free<T, untracked_t>::is_valid
+      >::type* = 0,
+      typename enable_if<
+        !can_query<T, tracked_t<I> >::value
+      >::type* = 0) ASIO_NOEXCEPT
+  {
+    return untracked_t();
+  }
+
+  template <typename E, typename T = decltype(untracked_t::static_query<E>())>
+  static ASIO_CONSTEXPR const T static_query_v
+    = untracked_t::static_query<E>();
+#endif // defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+  static ASIO_CONSTEXPR outstanding_work_t<I> value()
+  {
+    return untracked_t();
+  }
+
+  friend ASIO_CONSTEXPR bool operator==(
+      const untracked_t&, const untracked_t&)
+  {
+    return true;
+  }
+
+  friend ASIO_CONSTEXPR bool operator!=(
+      const untracked_t&, const untracked_t&)
+  {
+    return false;
+  }
+};
+
+#if defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+template <int I> template <typename E, typename T>
+const T untracked_t<I>::static_query_v;
+#endif // defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+template <int I = 0>
+struct tracked_t
+{
+#if defined(ASIO_HAS_VARIABLE_TEMPLATES)
+  template <typename T>
+  ASIO_STATIC_CONSTEXPR(bool,
+    is_applicable_property_v = (
+      is_executor<T>::value
+        || conditional<
+            is_executor<T>::value,
+            false_type,
+            is_sender<T>
+          >::type::value
+        || conditional<
+            is_executor<T>::value,
+            false_type,
+            is_scheduler<T>
+          >::type::value));
+#endif // defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+  ASIO_STATIC_CONSTEXPR(bool, is_requirable = true);
+  ASIO_STATIC_CONSTEXPR(bool, is_preferable = true);
+  typedef outstanding_work_t<I> polymorphic_query_result_type;
+
+  ASIO_CONSTEXPR tracked_t()
+  {
+  }
+
+  template <typename T>
+  struct query_member :
+    traits::query_member<
+      typename outstanding_work_t<I>::template proxy<T>::type, tracked_t> {};
+
+  template <typename T>
+  struct query_static_constexpr_member :
+    traits::query_static_constexpr_member<
+      typename outstanding_work_t<I>::template static_proxy<T>::type,
+        tracked_t> {};
+
+#if defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+  template <typename T>
+  static ASIO_CONSTEXPR
+  typename query_static_constexpr_member<T>::result_type
+  static_query()
+    ASIO_NOEXCEPT_IF((
+      query_static_constexpr_member<T>::is_noexcept))
+  {
+    return query_static_constexpr_member<T>::value();
+  }
+
+  template <typename E, typename T = decltype(tracked_t::static_query<E>())>
+  static ASIO_CONSTEXPR const T static_query_v
+    = tracked_t::static_query<E>();
+#endif // defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+  static ASIO_CONSTEXPR outstanding_work_t<I> value()
+  {
+    return tracked_t();
+  }
+
+  friend ASIO_CONSTEXPR bool operator==(
+      const tracked_t&, const tracked_t&)
+  {
+    return true;
+  }
+
+  friend ASIO_CONSTEXPR bool operator!=(
+      const tracked_t&, const tracked_t&)
+  {
+    return false;
+  }
+};
+
+#if defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+template <int I> template <typename E, typename T>
+const T tracked_t<I>::static_query_v;
+#endif // defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+} // namespace outstanding_work
+} // namespace detail
+
+typedef detail::outstanding_work_t<> outstanding_work_t;
+
+#if defined(ASIO_HAS_CONSTEXPR) || defined(GENERATING_DOCUMENTATION)
+constexpr outstanding_work_t outstanding_work;
+#else // defined(ASIO_HAS_CONSTEXPR) || defined(GENERATING_DOCUMENTATION)
+namespace { static const outstanding_work_t&
+  outstanding_work = outstanding_work_t::instance; }
+#endif
+
+} // namespace execution
+
+#if !defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename T>
+struct is_applicable_property<T, execution::outstanding_work_t>
+  : integral_constant<bool,
+      execution::is_executor<T>::value
+        || conditional<
+            execution::is_executor<T>::value,
+            false_type,
+            execution::is_sender<T>
+          >::type::value
+        || conditional<
+            execution::is_executor<T>::value,
+            false_type,
+            execution::is_scheduler<T>
+          >::type::value>
+{
+};
+
+template <typename T>
+struct is_applicable_property<T, execution::outstanding_work_t::untracked_t>
+  : integral_constant<bool,
+      execution::is_executor<T>::value
+        || conditional<
+            execution::is_executor<T>::value,
+            false_type,
+            execution::is_sender<T>
+          >::type::value
+        || conditional<
+            execution::is_executor<T>::value,
+            false_type,
+            execution::is_scheduler<T>
+          >::type::value>
+{
+};
+
+template <typename T>
+struct is_applicable_property<T, execution::outstanding_work_t::tracked_t>
+  : integral_constant<bool,
+      execution::is_executor<T>::value
+        || conditional<
+            execution::is_executor<T>::value,
+            false_type,
+            execution::is_sender<T>
+          >::type::value
+        || conditional<
+            execution::is_executor<T>::value,
+            false_type,
+            execution::is_scheduler<T>
+          >::type::value>
+{
+};
+
+#endif // !defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+namespace traits {
+
+#if !defined(ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+template <typename T>
+struct query_free_default<T, execution::outstanding_work_t,
+  typename enable_if<
+    can_query<T, execution::outstanding_work_t::untracked_t>::value
+  >::type>
+{
+  ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept =
+    (is_nothrow_query<T, execution::outstanding_work_t::untracked_t>::value));
+
+  typedef execution::outstanding_work_t result_type;
+};
+
+template <typename T>
+struct query_free_default<T, execution::outstanding_work_t,
+  typename enable_if<
+    !can_query<T, execution::outstanding_work_t::untracked_t>::value
+      && can_query<T, execution::outstanding_work_t::tracked_t>::value
+  >::type>
+{
+  ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept =
+    (is_nothrow_query<T, execution::outstanding_work_t::tracked_t>::value));
+
+  typedef execution::outstanding_work_t result_type;
+};
+
+#endif // !defined(ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+#if !defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  || !defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+template <typename T>
+struct static_query<T, execution::outstanding_work_t,
+  typename enable_if<
+    execution::detail::outstanding_work_t<0>::
+      query_static_constexpr_member<T>::is_valid
+  >::type>
+{
+  ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename execution::detail::outstanding_work_t<0>::
+    query_static_constexpr_member<T>::result_type result_type;
+
+  static ASIO_CONSTEXPR result_type value()
+  {
+    return execution::detail::outstanding_work_t<0>::
+      query_static_constexpr_member<T>::value();
+  }
+};
+
+template <typename T>
+struct static_query<T, execution::outstanding_work_t,
+  typename enable_if<
+    !execution::detail::outstanding_work_t<0>::
+        query_static_constexpr_member<T>::is_valid
+      && !execution::detail::outstanding_work_t<0>::
+        query_member<T>::is_valid
+      && traits::static_query<T,
+        execution::outstanding_work_t::untracked_t>::is_valid
+  >::type>
+{
+  ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename traits::static_query<T,
+    execution::outstanding_work_t::untracked_t>::result_type result_type;
+
+  static ASIO_CONSTEXPR result_type value()
+  {
+    return traits::static_query<T,
+        execution::outstanding_work_t::untracked_t>::value();
+  }
+};
+
+template <typename T>
+struct static_query<T, execution::outstanding_work_t,
+  typename enable_if<
+    !execution::detail::outstanding_work_t<0>::
+        query_static_constexpr_member<T>::is_valid
+      && !execution::detail::outstanding_work_t<0>::
+        query_member<T>::is_valid
+      && !traits::static_query<T,
+        execution::outstanding_work_t::untracked_t>::is_valid
+      && traits::static_query<T,
+        execution::outstanding_work_t::tracked_t>::is_valid
+  >::type>
+{
+  ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename traits::static_query<T,
+    execution::outstanding_work_t::tracked_t>::result_type result_type;
+
+  static ASIO_CONSTEXPR result_type value()
+  {
+    return traits::static_query<T,
+        execution::outstanding_work_t::tracked_t>::value();
+  }
+};
+
+template <typename T>
+struct static_query<T, execution::outstanding_work_t::untracked_t,
+  typename enable_if<
+    execution::detail::outstanding_work::untracked_t<0>::
+      query_static_constexpr_member<T>::is_valid
+  >::type>
+{
+  ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename execution::detail::outstanding_work::untracked_t<0>::
+    query_static_constexpr_member<T>::result_type result_type;
+
+  static ASIO_CONSTEXPR result_type value()
+  {
+    return execution::detail::outstanding_work::untracked_t<0>::
+      query_static_constexpr_member<T>::value();
+  }
+};
+
+template <typename T>
+struct static_query<T, execution::outstanding_work_t::untracked_t,
+  typename enable_if<
+    !execution::detail::outstanding_work::untracked_t<0>::
+        query_static_constexpr_member<T>::is_valid
+      && !execution::detail::outstanding_work::untracked_t<0>::
+          query_member<T>::is_valid
+      && !traits::query_free<T,
+        execution::outstanding_work_t::untracked_t>::is_valid
+      && !can_query<T, execution::outstanding_work_t::tracked_t>::value
+  >::type>
+{
+  ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef execution::outstanding_work_t::untracked_t result_type;
+
+  static ASIO_CONSTEXPR result_type value()
+  {
+    return result_type();
+  }
+};
+
+template <typename T>
+struct static_query<T, execution::outstanding_work_t::tracked_t,
+  typename enable_if<
+    execution::detail::outstanding_work::tracked_t<0>::
+      query_static_constexpr_member<T>::is_valid
+  >::type>
+{
+  ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename execution::detail::outstanding_work::tracked_t<0>::
+    query_static_constexpr_member<T>::result_type result_type;
+
+  static ASIO_CONSTEXPR result_type value()
+  {
+    return execution::detail::outstanding_work::tracked_t<0>::
+      query_static_constexpr_member<T>::value();
+  }
+};
+
+#endif // !defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   || !defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+#if !defined(ASIO_HAS_DEDUCED_STATIC_REQUIRE_TRAIT)
+
+template <typename T>
+struct static_require<T, execution::outstanding_work_t::untracked_t,
+  typename enable_if<
+    static_query<T, execution::outstanding_work_t::untracked_t>::is_valid
+  >::type>
+{
+  ASIO_STATIC_CONSTEXPR(bool, is_valid =
+    (is_same<typename static_query<T,
+      execution::outstanding_work_t::untracked_t>::result_type,
+        execution::outstanding_work_t::untracked_t>::value));
+};
+
+template <typename T>
+struct static_require<T, execution::outstanding_work_t::tracked_t,
+  typename enable_if<
+    static_query<T, execution::outstanding_work_t::tracked_t>::is_valid
+  >::type>
+{
+  ASIO_STATIC_CONSTEXPR(bool, is_valid =
+    (is_same<typename static_query<T,
+      execution::outstanding_work_t::tracked_t>::result_type,
+        execution::outstanding_work_t::tracked_t>::value));
+};
+
+#endif // !defined(ASIO_HAS_DEDUCED_STATIC_REQUIRE_TRAIT)
+
+} // namespace traits
+
+#endif // defined(GENERATING_DOCUMENTATION)
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_EXECUTION_OUTSTANDING_WORK_HPP

extern/asio-1.18.2/include/asio/execution/prefer_only.hpp

@@ -0,0 +1,331 @@
+//
+// execution/prefer_only.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2021 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_EXECUTION_PREFER_ONLY_HPP
+#define ASIO_EXECUTION_PREFER_ONLY_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/detail/type_traits.hpp"
+#include "asio/is_applicable_property.hpp"
+#include "asio/prefer.hpp"
+#include "asio/query.hpp"
+#include "asio/traits/static_query.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+
+#if defined(GENERATING_DOCUMENTATION)
+
+namespace execution {
+
+/// A property adapter that is used with the polymorphic executor wrapper
+/// to mark properties as preferable, but not requirable.
+template <typename Property>
+struct prefer_only
+{
+  /// The prefer_only adapter applies to the same types as the nested property.
+  template <typename T>
+  static constexpr bool is_applicable_property_v =
+    is_applicable_property<T, Property>::value;
+
+  /// The context_t property cannot be required.
+  static constexpr bool is_requirable = false;
+
+  /// The context_t property can be preferred, it the underlying property can
+  /// be preferred.
+  /**
+   * @c true if @c Property::is_preferable is @c true, otherwise @c false.
+   */
+  static constexpr bool is_preferable = automatically_determined;
+
+  /// The type returned by queries against an @c any_executor.
+  typedef typename Property::polymorphic_query_result_type
+    polymorphic_query_result_type;
+};
+
+} // namespace execution
+
+#else // defined(GENERATING_DOCUMENTATION)
+
+namespace execution {
+namespace detail {
+
+template <typename InnerProperty, typename = void>
+struct prefer_only_is_preferable
+{
+  ASIO_STATIC_CONSTEXPR(bool, is_preferable = false);
+};
+
+template <typename InnerProperty>
+struct prefer_only_is_preferable<InnerProperty,
+    typename enable_if<
+      InnerProperty::is_preferable
+    >::type>
+{
+  ASIO_STATIC_CONSTEXPR(bool, is_preferable = true);
+};
+
+template <typename InnerProperty, typename = void>
+struct prefer_only_polymorphic_query_result_type
+{
+};
+
+template <typename InnerProperty>
+struct prefer_only_polymorphic_query_result_type<InnerProperty,
+    typename void_type<
+      typename InnerProperty::polymorphic_query_result_type
+    >::type>
+{
+  typedef typename InnerProperty::polymorphic_query_result_type
+    polymorphic_query_result_type;
+};
+
+template <typename InnerProperty, typename = void>
+struct prefer_only_property
+{
+  InnerProperty property;
+
+  prefer_only_property(const InnerProperty& p)
+    : property(p)
+  {
+  }
+};
+
+#if defined(ASIO_HAS_DECLTYPE) \
+  && defined(ASIO_HAS_WORKING_EXPRESSION_SFINAE)
+
+template <typename InnerProperty>
+struct prefer_only_property<InnerProperty,
+    typename void_type<
+      decltype(asio::declval<const InnerProperty>().value())
+    >::type>
+{
+  InnerProperty property;
+
+  prefer_only_property(const InnerProperty& p)
+    : property(p)
+  {
+  }
+
+  ASIO_CONSTEXPR auto value() const
+    ASIO_NOEXCEPT_IF((
+      noexcept(asio::declval<const InnerProperty>().value())))
+    -> decltype(asio::declval<const InnerProperty>().value())
+  {
+    return property.value();
+  }
+};
+
+#else // defined(ASIO_HAS_DECLTYPE)
+      //   && defined(ASIO_HAS_WORKING_EXPRESSION_SFINAE)
+
+struct prefer_only_memfns_base
+{
+  void value();
+};
+
+template <typename T>
+struct prefer_only_memfns_derived
+  : T, prefer_only_memfns_base
+{
+};
+
+template <typename T, T>
+struct prefer_only_memfns_check
+{
+};
+
+template <typename>
+char (&prefer_only_value_memfn_helper(...))[2];
+
+template <typename T>
+char prefer_only_value_memfn_helper(
+    prefer_only_memfns_check<
+      void (prefer_only_memfns_base::*)(),
+      &prefer_only_memfns_derived<T>::value>*);
+
+template <typename InnerProperty>
+struct prefer_only_property<InnerProperty,
+    typename enable_if<
+      sizeof(prefer_only_value_memfn_helper<InnerProperty>(0)) != 1
+        && !is_same<typename InnerProperty::polymorphic_query_result_type,
+          void>::value
+    >::type>
+{
+  InnerProperty property;
+
+  prefer_only_property(const InnerProperty& p)
+    : property(p)
+  {
+  }
+
+  ASIO_CONSTEXPR typename InnerProperty::polymorphic_query_result_type
+  value() const
+  {
+    return property.value();
+  }
+};
+
+#endif // defined(ASIO_HAS_DECLTYPE)
+       //   && defined(ASIO_HAS_WORKING_EXPRESSION_SFINAE)
+
+} // namespace detail
+
+template <typename InnerProperty>
+struct prefer_only :
+  detail::prefer_only_is_preferable<InnerProperty>,
+  detail::prefer_only_polymorphic_query_result_type<InnerProperty>,
+  detail::prefer_only_property<InnerProperty>
+{
+  ASIO_STATIC_CONSTEXPR(bool, is_requirable = false);
+
+  ASIO_CONSTEXPR prefer_only(const InnerProperty& p)
+    : detail::prefer_only_property<InnerProperty>(p)
+  {
+  }
+
+#if defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+  template <typename T>
+  static ASIO_CONSTEXPR
+  typename traits::static_query<T, InnerProperty>::result_type
+  static_query()
+    ASIO_NOEXCEPT_IF((
+      traits::static_query<T, InnerProperty>::is_noexcept))
+  {
+    return traits::static_query<T, InnerProperty>::value();
+  }
+
+  template <typename E, typename T = decltype(prefer_only::static_query<E>())>
+  static ASIO_CONSTEXPR const T static_query_v
+    = prefer_only::static_query<E>();
+#endif // defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+  template <typename Executor, typename Property>
+  friend ASIO_CONSTEXPR
+  typename prefer_result<const Executor&, const InnerProperty&>::type
+  prefer(const Executor& ex, const prefer_only<Property>& p,
+      typename enable_if<
+        is_same<Property, InnerProperty>::value
+      >::type* = 0,
+      typename enable_if<
+        can_prefer<const Executor&, const InnerProperty&>::value
+      >::type* = 0)
+#if !defined(ASIO_MSVC) \
+  && !defined(__clang__) // Clang crashes if noexcept is used here.
+    ASIO_NOEXCEPT_IF((
+      is_nothrow_prefer<const Executor&, const InnerProperty&>::value))
+#endif // !defined(ASIO_MSVC)
+       //   && !defined(__clang__)
+  {
+    return asio::prefer(ex, p.property);
+  }
+
+  template <typename Executor, typename Property>
+  friend ASIO_CONSTEXPR
+  typename query_result<const Executor&, const InnerProperty&>::type
+  query(const Executor& ex, const prefer_only<Property>& p,
+      typename enable_if<
+        is_same<Property, InnerProperty>::value
+      >::type* = 0,
+      typename enable_if<
+        can_query<const Executor&, const InnerProperty&>::value
+      >::type* = 0)
+#if !defined(ASIO_MSVC) \
+  && !defined(__clang__) // Clang crashes if noexcept is used here.
+    ASIO_NOEXCEPT_IF((
+      is_nothrow_query<const Executor&, const InnerProperty&>::value))
+#endif // !defined(ASIO_MSVC)
+       //   && !defined(__clang__)
+  {
+    return asio::query(ex, p.property);
+  }
+};
+
+#if defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+template <typename InnerProperty> template <typename E, typename T>
+const T prefer_only<InnerProperty>::static_query_v;
+#endif // defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+} // namespace execution
+
+template <typename T, typename InnerProperty>
+struct is_applicable_property<T, execution::prefer_only<InnerProperty> >
+  : is_applicable_property<T, InnerProperty>
+{
+};
+
+namespace traits {
+
+#if !defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  || !defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+template <typename T, typename InnerProperty>
+struct static_query<T, execution::prefer_only<InnerProperty> > :
+  static_query<T, const InnerProperty&>
+{
+};
+
+#endif // !defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   || !defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+#if !defined(ASIO_HAS_DEDUCED_PREFER_FREE_TRAIT)
+
+template <typename T, typename InnerProperty>
+struct prefer_free_default<T, execution::prefer_only<InnerProperty>,
+    typename enable_if<
+      can_prefer<const T&, const InnerProperty&>::value
+    >::type>
+{
+  ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept =
+    (is_nothrow_prefer<const T&, const InnerProperty&>::value));
+
+  typedef typename prefer_result<const T&,
+      const InnerProperty&>::type result_type;
+};
+
+#endif // !defined(ASIO_HAS_DEDUCED_PREFER_FREE_TRAIT)
+
+#if !defined(ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+template <typename T, typename InnerProperty>
+struct query_free<T, execution::prefer_only<InnerProperty>,
+    typename enable_if<
+      can_query<const T&, const InnerProperty&>::value
+    >::type>
+{
+  ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept =
+    (is_nothrow_query<const T&, const InnerProperty&>::value));
+
+  typedef typename query_result<const T&,
+      const InnerProperty&>::type result_type;
+};
+
+#endif // !defined(ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+} // namespace traits
+
+#endif // defined(GENERATING_DOCUMENTATION)
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_EXECUTION_PREFER_ONLY_HPP

extern/asio-1.18.2/include/asio/execution/receiver.hpp

@@ -0,0 +1,280 @@
+//
+// execution/receiver.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2021 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_EXECUTION_RECEIVER_HPP
+#define ASIO_EXECUTION_RECEIVER_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/detail/type_traits.hpp"
+#include "asio/detail/variadic_templates.hpp"
+#include "asio/execution/set_done.hpp"
+#include "asio/execution/set_error.hpp"
+#include "asio/execution/set_value.hpp"
+
+#if defined(ASIO_HAS_STD_EXCEPTION_PTR)
+# include <exception>
+#else // defined(ASIO_HAS_STD_EXCEPTION_PTR)
+# include "asio/error_code.hpp"
+#endif // defined(ASIO_HAS_STD_EXCEPTION_PTR)
+
+#if defined(ASIO_HAS_DEDUCED_SET_DONE_FREE_TRAIT) \
+  && defined(ASIO_HAS_DEDUCED_SET_DONE_MEMBER_TRAIT) \
+  && defined(ASIO_HAS_DEDUCED_SET_ERROR_FREE_TRAIT) \
+  && defined(ASIO_HAS_DEDUCED_SET_ERROR_MEMBER_TRAIT) \
+  && defined(ASIO_HAS_DEDUCED_SET_VALUE_FREE_TRAIT) \
+  && defined(ASIO_HAS_DEDUCED_SET_VALUE_MEMBER_TRAIT) \
+  && defined(ASIO_HAS_DEDUCED_RECEIVER_OF_FREE_TRAIT) \
+  && defined(ASIO_HAS_DEDUCED_RECEIVER_OF_MEMBER_TRAIT)
+# define ASIO_HAS_DEDUCED_EXECUTION_IS_RECEIVER_TRAIT 1
+#endif // defined(ASIO_HAS_DEDUCED_SET_DONE_FREE_TRAIT)
+       //   && defined(ASIO_HAS_DEDUCED_SET_DONE_MEMBER_TRAIT)
+       //   && defined(ASIO_HAS_DEDUCED_SET_ERROR_FREE_TRAIT)
+       //   && defined(ASIO_HAS_DEDUCED_SET_ERROR_MEMBER_TRAIT)
+       //   && defined(ASIO_HAS_DEDUCED_SET_VALUE_FREE_TRAIT)
+       //   && defined(ASIO_HAS_DEDUCED_SET_VALUE_MEMBER_TRAIT)
+       //   && defined(ASIO_HAS_DEDUCED_RECEIVER_OF_FREE_TRAIT)
+       //   && defined(ASIO_HAS_DEDUCED_RECEIVER_OF_MEMBER_TRAIT)
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace execution {
+namespace detail {
+
+template <typename T, typename E>
+struct is_receiver_base :
+  integral_constant<bool,
+    is_move_constructible<typename remove_cvref<T>::type>::value
+      && is_constructible<typename remove_cvref<T>::type, T>::value
+  >
+{
+};
+
+} // namespace detail
+
+#if defined(ASIO_HAS_STD_EXCEPTION_PTR)
+# define ASIO_EXECUTION_RECEIVER_ERROR_DEFAULT = std::exception_ptr
+#else // defined(ASIO_HAS_STD_EXCEPTION_PTR)
+# define ASIO_EXECUTION_RECEIVER_ERROR_DEFAULT \
+  = ::asio::error_code
+#endif // defined(ASIO_HAS_STD_EXCEPTION_PTR)
+
+/// The is_receiver trait detects whether a type T satisfies the
+/// execution::receiver concept.
+/**
+ * Class template @c is_receiver is a type trait that is derived from @c
+ * true_type if the type @c T meets the concept definition for a receiver for
+ * error type @c E, otherwise @c false_type.
+ */
+template <typename T, typename E ASIO_EXECUTION_RECEIVER_ERROR_DEFAULT>
+struct is_receiver :
+#if defined(GENERATING_DOCUMENTATION)
+  integral_constant<bool, automatically_determined>
+#else // defined(GENERATING_DOCUMENTATION)
+  conditional<
+    can_set_done<typename remove_cvref<T>::type>::value
+      && is_nothrow_set_done<typename remove_cvref<T>::type>::value
+      && can_set_error<typename remove_cvref<T>::type, E>::value
+      && is_nothrow_set_error<typename remove_cvref<T>::type, E>::value,
+    detail::is_receiver_base<T, E>,
+    false_type
+  >::type
+#endif // defined(GENERATING_DOCUMENTATION)
+{
+};
+
+#if defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename T, typename E ASIO_EXECUTION_RECEIVER_ERROR_DEFAULT>
+ASIO_CONSTEXPR const bool is_receiver_v = is_receiver<T, E>::value;
+
+#endif // defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+#if defined(ASIO_HAS_CONCEPTS)
+
+template <typename T, typename E ASIO_EXECUTION_RECEIVER_ERROR_DEFAULT>
+ASIO_CONCEPT receiver = is_receiver<T, E>::value;
+
+#define ASIO_EXECUTION_RECEIVER ::asio::execution::receiver
+
+#else // defined(ASIO_HAS_CONCEPTS)
+
+#define ASIO_EXECUTION_RECEIVER typename
+
+#endif // defined(ASIO_HAS_CONCEPTS)
+
+#if defined(ASIO_HAS_VARIADIC_TEMPLATES) \
+  || defined(GENERATING_DOCUMENTATION)
+
+/// The is_receiver_of trait detects whether a type T satisfies the
+/// execution::receiver_of concept for some set of value arguments.
+/**
+ * Class template @c is_receiver_of is a type trait that is derived from @c
+ * true_type if the type @c T meets the concept definition for a receiver for
+ * value arguments @c Vs, otherwise @c false_type.
+ */
+template <typename T, typename... Vs>
+struct is_receiver_of :
+#if defined(GENERATING_DOCUMENTATION)
+  integral_constant<bool, automatically_determined>
+#else // defined(GENERATING_DOCUMENTATION)
+  conditional<
+    is_receiver<T>::value,
+    can_set_value<typename remove_cvref<T>::type, Vs...>,
+    false_type
+  >::type
+#endif // defined(GENERATING_DOCUMENTATION)
+{
+};
+
+#if defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename T, typename... Vs>
+ASIO_CONSTEXPR const bool is_receiver_of_v =
+  is_receiver_of<T, Vs...>::value;
+
+#endif // defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+#if defined(ASIO_HAS_CONCEPTS)
+
+template <typename T, typename... Vs>
+ASIO_CONCEPT receiver_of = is_receiver_of<T, Vs...>::value;
+
+#define ASIO_EXECUTION_RECEIVER_OF_0 \
+  ::asio::execution::receiver_of
+
+#define ASIO_EXECUTION_RECEIVER_OF_1(v) \
+  ::asio::execution::receiver_of<v>
+
+#else // defined(ASIO_HAS_CONCEPTS)
+
+#define ASIO_EXECUTION_RECEIVER_OF_0 typename
+#define ASIO_EXECUTION_RECEIVER_OF_1(v) typename
+
+#endif // defined(ASIO_HAS_CONCEPTS)
+
+#else // defined(ASIO_HAS_VARIADIC_TEMPLATES)
+      //   || defined(GENERATING_DOCUMENTATION)
+
+template <typename T, typename = void,
+    typename = void, typename = void, typename = void, typename = void,
+    typename = void, typename = void, typename = void, typename = void>
+struct is_receiver_of;
+
+template <typename T>
+struct is_receiver_of<T> :
+  conditional<
+    is_receiver<T>::value,
+    can_set_value<typename remove_cvref<T>::type>,
+    false_type
+  >::type
+{
+};
+
+#define ASIO_PRIVATE_RECEIVER_OF_TRAITS_DEF(n) \
+  template <typename T, ASIO_VARIADIC_TPARAMS(n)> \
+  struct is_receiver_of<T, ASIO_VARIADIC_TARGS(n)> : \
+    conditional< \
+      conditional<true, is_receiver<T>, void>::type::value, \
+      can_set_value< \
+        typename remove_cvref<T>::type, \
+        ASIO_VARIADIC_TARGS(n)>, \
+      false_type \
+    >::type \
+  { \
+  }; \
+  /**/
+ASIO_VARIADIC_GENERATE(ASIO_PRIVATE_RECEIVER_OF_TRAITS_DEF)
+#undef ASIO_PRIVATE_RECEIVER_OF_TRAITS_DEF
+
+#define ASIO_EXECUTION_RECEIVER_OF_0 typename
+#define ASIO_EXECUTION_RECEIVER_OF_1(v) typename
+
+#endif // defined(ASIO_HAS_VARIADIC_TEMPLATES)
+       //   || defined(GENERATING_DOCUMENTATION)
+
+#if defined(ASIO_HAS_VARIADIC_TEMPLATES) \
+  || defined(GENERATING_DOCUMENTATION)
+
+/// The is_nothrow_receiver_of trait detects whether a type T satisfies the
+/// execution::receiver_of concept for some set of value arguments, with a
+/// noexcept @c set_value operation.
+/**
+ * Class template @c is_nothrow_receiver_of is a type trait that is derived
+ * from @c true_type if the type @c T meets the concept definition for a
+ * receiver for value arguments @c Vs, and the expression
+ * <tt>execution::set_value(declval<T>(), declval<Ts>()...)</tt> is noexcept,
+ * otherwise @c false_type.
+ */
+template <typename T, typename... Vs>
+struct is_nothrow_receiver_of :
+#if defined(GENERATING_DOCUMENTATION)
+  integral_constant<bool, automatically_determined>
+#else // defined(GENERATING_DOCUMENTATION)
+  integral_constant<bool,
+    is_receiver_of<T, Vs...>::value
+      && is_nothrow_set_value<typename remove_cvref<T>::type, Vs...>::value
+  >
+#endif // defined(GENERATING_DOCUMENTATION)
+{
+};
+
+#if defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename T, typename... Vs>
+ASIO_CONSTEXPR const bool is_nothrow_receiver_of_v =
+  is_nothrow_receiver_of<T, Vs...>::value;
+
+#endif // defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+#else // defined(ASIO_HAS_VARIADIC_TEMPLATES)
+      //   || defined(GENERATING_DOCUMENTATION)
+
+template <typename T, typename = void,
+    typename = void, typename = void, typename = void, typename = void,
+    typename = void, typename = void, typename = void, typename = void>
+struct is_nothrow_receiver_of;
+
+template <typename T>
+struct is_nothrow_receiver_of<T> :
+  integral_constant<bool,
+    is_receiver_of<T>::value
+      && is_nothrow_set_value<typename remove_cvref<T>::type>::value
+  >
+{
+};
+
+#define ASIO_PRIVATE_NOTHROW_RECEIVER_OF_TRAITS_DEF(n) \
+  template <typename T, ASIO_VARIADIC_TPARAMS(n)> \
+  struct is_nothrow_receiver_of<T, ASIO_VARIADIC_TARGS(n)> : \
+    integral_constant<bool, \
+      is_receiver_of<T, ASIO_VARIADIC_TARGS(n)>::value \
+        && is_nothrow_set_value<typename remove_cvref<T>::type, \
+          ASIO_VARIADIC_TARGS(n)>::value \
+    > \
+  { \
+  }; \
+  /**/
+ASIO_VARIADIC_GENERATE(ASIO_PRIVATE_NOTHROW_RECEIVER_OF_TRAITS_DEF)
+#undef ASIO_PRIVATE_NOTHROW_RECEIVER_OF_TRAITS_DEF
+
+#endif // defined(ASIO_HAS_VARIADIC_TEMPLATES)
+       //   || defined(GENERATING_DOCUMENTATION)
+
+} // namespace execution
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_EXECUTION_RECEIVER_HPP

extern/asio-1.18.2/include/asio/execution/receiver_invocation_error.hpp

@@ -0,0 +1,48 @@
+//
+// execution/receiver_invocation_error.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2021 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_EXECUTION_RECEIVER_INVOCATION_ERROR_HPP
+#define ASIO_EXECUTION_RECEIVER_INVOCATION_ERROR_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include <stdexcept>
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace execution {
+
+/// Exception reported via @c set_error when an exception escapes from
+/// @c set_value.
+class receiver_invocation_error
+  : public std::runtime_error
+#if defined(ASIO_HAS_STD_NESTED_EXCEPTION)
+  , public std::nested_exception
+#endif // defined(ASIO_HAS_STD_NESTED_EXCEPTION)
+{
+public:
+  /// Constructor.
+  ASIO_DECL receiver_invocation_error();
+};
+
+} // namespace execution
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#if defined(ASIO_HEADER_ONLY)
+# include "asio/execution/impl/receiver_invocation_error.ipp"
+#endif // defined(ASIO_HEADER_ONLY)
+
+#endif // ASIO_EXECUTION_RECEIVER_INVOCATION_ERROR_HPP

extern/asio-1.18.2/include/asio/execution/relationship.hpp

@@ -0,0 +1,865 @@
+//
+// execution/relationship.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2021 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_EXECUTION_RELATIONSHIP_HPP
+#define ASIO_EXECUTION_RELATIONSHIP_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/detail/type_traits.hpp"
+#include "asio/execution/executor.hpp"
+#include "asio/execution/scheduler.hpp"
+#include "asio/execution/sender.hpp"
+#include "asio/is_applicable_property.hpp"
+#include "asio/query.hpp"
+#include "asio/traits/query_free.hpp"
+#include "asio/traits/query_member.hpp"
+#include "asio/traits/query_static_constexpr_member.hpp"
+#include "asio/traits/static_query.hpp"
+#include "asio/traits/static_require.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+
+#if defined(GENERATING_DOCUMENTATION)
+
+namespace execution {
+
+/// A property to describe whether submitted tasks represent continuations of
+/// the calling context.
+struct relationship_t
+{
+  /// The relationship_t property applies to executors, senders, and schedulers.
+  template <typename T>
+  static constexpr bool is_applicable_property_v =
+    is_executor_v<T> || is_sender_v<T> || is_scheduler_v<T>;
+
+  /// The top-level relationship_t property cannot be required.
+  static constexpr bool is_requirable = false;
+
+  /// The top-level relationship_t property cannot be preferred.
+  static constexpr bool is_preferable = false;
+
+  /// The type returned by queries against an @c any_executor.
+  typedef relationship_t polymorphic_query_result_type;
+
+  /// A sub-property that indicates that the executor does not represent a
+  /// continuation of the calling context.
+  struct fork_t
+  {
+    /// The relationship_t::fork_t property applies to executors, senders, and
+    /// schedulers.
+    template <typename T>
+    static constexpr bool is_applicable_property_v =
+      is_executor_v<T> || is_sender_v<T> || is_scheduler_v<T>;
+
+    /// The relationship_t::fork_t property can be required.
+    static constexpr bool is_requirable = true;
+
+    /// The relationship_t::fork_t property can be preferred.
+    static constexpr bool is_preferable = true;
+
+    /// The type returned by queries against an @c any_executor.
+    typedef relationship_t polymorphic_query_result_type;
+
+    /// Default constructor.
+    constexpr fork_t();
+
+    /// Get the value associated with a property object.
+    /**
+     * @returns fork_t();
+     */
+    static constexpr relationship_t value();
+  };
+
+  /// A sub-property that indicates that the executor represents a continuation
+  /// of the calling context.
+  struct continuation_t
+  {
+    /// The relationship_t::continuation_t property applies to executors,
+    /// senders, and schedulers.
+    template <typename T>
+    static constexpr bool is_applicable_property_v =
+      is_executor_v<T> || is_sender_v<T> || is_scheduler_v<T>;
+
+    /// The relationship_t::continuation_t property can be required.
+    static constexpr bool is_requirable = true;
+
+    /// The relationship_t::continuation_t property can be preferred.
+    static constexpr bool is_preferable = true;
+
+    /// The type returned by queries against an @c any_executor.
+    typedef relationship_t polymorphic_query_result_type;
+
+    /// Default constructor.
+    constexpr continuation_t();
+
+    /// Get the value associated with a property object.
+    /**
+     * @returns continuation_t();
+     */
+    static constexpr relationship_t value();
+  };
+
+  /// A special value used for accessing the relationship_t::fork_t property.
+  static constexpr fork_t fork;
+
+  /// A special value used for accessing the relationship_t::continuation_t
+  /// property.
+  static constexpr continuation_t continuation;
+
+  /// Default constructor.
+  constexpr relationship_t();
+
+  /// Construct from a sub-property value.
+  constexpr relationship_t(fork_t);
+
+  /// Construct from a sub-property value.
+  constexpr relationship_t(continuation_t);
+
+  /// Compare property values for equality.
+  friend constexpr bool operator==(
+      const relationship_t& a, const relationship_t& b) noexcept;
+
+  /// Compare property values for inequality.
+  friend constexpr bool operator!=(
+      const relationship_t& a, const relationship_t& b) noexcept;
+};
+
+/// A special value used for accessing the relationship_t property.
+constexpr relationship_t relationship;
+
+} // namespace execution
+
+#else // defined(GENERATING_DOCUMENTATION)
+
+namespace execution {
+namespace detail {
+namespace relationship {
+
+template <int I> struct fork_t;
+template <int I> struct continuation_t;
+
+} // namespace relationship
+
+template <int I = 0>
+struct relationship_t
+{
+#if defined(ASIO_HAS_VARIABLE_TEMPLATES)
+  template <typename T>
+  ASIO_STATIC_CONSTEXPR(bool,
+    is_applicable_property_v = (
+      is_executor<T>::value
+        || conditional<
+            is_executor<T>::value,
+            false_type,
+            is_sender<T>
+          >::type::value
+        || conditional<
+            is_executor<T>::value,
+            false_type,
+            is_scheduler<T>
+          >::type::value));
+#endif // defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+  ASIO_STATIC_CONSTEXPR(bool, is_requirable = false);
+  ASIO_STATIC_CONSTEXPR(bool, is_preferable = false);
+  typedef relationship_t polymorphic_query_result_type;
+
+  typedef detail::relationship::fork_t<I> fork_t;
+  typedef detail::relationship::continuation_t<I> continuation_t;
+
+  ASIO_CONSTEXPR relationship_t()
+    : value_(-1)
+  {
+  }
+
+  ASIO_CONSTEXPR relationship_t(fork_t)
+    : value_(0)
+  {
+  }
+
+  ASIO_CONSTEXPR relationship_t(continuation_t)
+    : value_(1)
+  {
+  }
+
+  template <typename T>
+  struct proxy
+  {
+#if defined(ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
+    struct type
+    {
+      template <typename P>
+      auto query(ASIO_MOVE_ARG(P) p) const
+        noexcept(
+          noexcept(
+            declval<typename conditional<true, T, P>::type>().query(
+              ASIO_MOVE_CAST(P)(p))
+          )
+        )
+        -> decltype(
+          declval<typename conditional<true, T, P>::type>().query(
+            ASIO_MOVE_CAST(P)(p))
+        );
+    };
+#else // defined(ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
+    typedef T type;
+#endif // defined(ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
+  };
+
+  template <typename T>
+  struct static_proxy
+  {
+#if defined(ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
+    struct type
+    {
+      template <typename P>
+      static constexpr auto query(ASIO_MOVE_ARG(P) p)
+        noexcept(
+          noexcept(
+            conditional<true, T, P>::type::query(ASIO_MOVE_CAST(P)(p))
+          )
+        )
+        -> decltype(
+          conditional<true, T, P>::type::query(ASIO_MOVE_CAST(P)(p))
+        )
+      {
+        return T::query(ASIO_MOVE_CAST(P)(p));
+      }
+    };
+#else // defined(ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
+    typedef T type;
+#endif // defined(ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
+  };
+
+  template <typename T>
+  struct query_member :
+    traits::query_member<typename proxy<T>::type, relationship_t> {};
+
+  template <typename T>
+  struct query_static_constexpr_member :
+    traits::query_static_constexpr_member<
+      typename static_proxy<T>::type, relationship_t> {};
+
+#if defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+  template <typename T>
+  static ASIO_CONSTEXPR
+  typename query_static_constexpr_member<T>::result_type
+  static_query()
+    ASIO_NOEXCEPT_IF((
+      query_static_constexpr_member<T>::is_noexcept))
+  {
+    return query_static_constexpr_member<T>::value();
+  }
+
+  template <typename T>
+  static ASIO_CONSTEXPR
+  typename traits::static_query<T, fork_t>::result_type
+  static_query(
+      typename enable_if<
+        !query_static_constexpr_member<T>::is_valid
+      >::type* = 0,
+      typename enable_if<
+        !query_member<T>::is_valid
+      >::type* = 0,
+      typename enable_if<
+        traits::static_query<T, fork_t>::is_valid
+      >::type* = 0) ASIO_NOEXCEPT
+  {
+    return traits::static_query<T, fork_t>::value();
+  }
+
+  template <typename T>
+  static ASIO_CONSTEXPR
+  typename traits::static_query<T, continuation_t>::result_type
+  static_query(
+      typename enable_if<
+        !query_static_constexpr_member<T>::is_valid
+      >::type* = 0,
+      typename enable_if<
+        !query_member<T>::is_valid
+      >::type* = 0,
+      typename enable_if<
+        !traits::static_query<T, fork_t>::is_valid
+      >::type* = 0,
+      typename enable_if<
+        traits::static_query<T, continuation_t>::is_valid
+      >::type* = 0) ASIO_NOEXCEPT
+  {
+    return traits::static_query<T, continuation_t>::value();
+  }
+
+  template <typename E,
+      typename T = decltype(relationship_t::static_query<E>())>
+  static ASIO_CONSTEXPR const T static_query_v
+    = relationship_t::static_query<E>();
+#endif // defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+  friend ASIO_CONSTEXPR bool operator==(
+      const relationship_t& a, const relationship_t& b)
+  {
+    return a.value_ == b.value_;
+  }
+
+  friend ASIO_CONSTEXPR bool operator!=(
+      const relationship_t& a, const relationship_t& b)
+  {
+    return a.value_ != b.value_;
+  }
+
+  struct convertible_from_relationship_t
+  {
+    ASIO_CONSTEXPR convertible_from_relationship_t(relationship_t)
+    {
+    }
+  };
+
+  template <typename Executor>
+  friend ASIO_CONSTEXPR relationship_t query(
+      const Executor& ex, convertible_from_relationship_t,
+      typename enable_if<
+        can_query<const Executor&, fork_t>::value
+      >::type* = 0)
+#if !defined(__clang__) // Clang crashes if noexcept is used here.
+#if defined(ASIO_MSVC) // Visual C++ wants the type to be qualified.
+    ASIO_NOEXCEPT_IF((
+      is_nothrow_query<const Executor&, relationship_t<>::fork_t>::value))
+#else // defined(ASIO_MSVC)
+    ASIO_NOEXCEPT_IF((
+      is_nothrow_query<const Executor&, fork_t>::value))
+#endif // defined(ASIO_MSVC)
+#endif // !defined(__clang__)
+  {
+    return asio::query(ex, fork_t());
+  }
+
+  template <typename Executor>
+  friend ASIO_CONSTEXPR relationship_t query(
+      const Executor& ex, convertible_from_relationship_t,
+      typename enable_if<
+        !can_query<const Executor&, fork_t>::value
+      >::type* = 0,
+      typename enable_if<
+        can_query<const Executor&, continuation_t>::value
+      >::type* = 0)
+#if !defined(__clang__) // Clang crashes if noexcept is used here.
+#if defined(ASIO_MSVC) // Visual C++ wants the type to be qualified.
+    ASIO_NOEXCEPT_IF((
+      is_nothrow_query<const Executor&,
+        relationship_t<>::continuation_t>::value))
+#else // defined(ASIO_MSVC)
+    ASIO_NOEXCEPT_IF((
+      is_nothrow_query<const Executor&, continuation_t>::value))
+#endif // defined(ASIO_MSVC)
+#endif // !defined(__clang__)
+  {
+    return asio::query(ex, continuation_t());
+  }
+
+  ASIO_STATIC_CONSTEXPR_DEFAULT_INIT(fork_t, fork);
+  ASIO_STATIC_CONSTEXPR_DEFAULT_INIT(continuation_t, continuation);
+
+#if !defined(ASIO_HAS_CONSTEXPR)
+  static const relationship_t instance;
+#endif // !defined(ASIO_HAS_CONSTEXPR)
+
+private:
+  int value_;
+};
+
+#if defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+template <int I> template <typename E, typename T>
+const T relationship_t<I>::static_query_v;
+#endif // defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+#if !defined(ASIO_HAS_CONSTEXPR)
+template <int I>
+const relationship_t<I> relationship_t<I>::instance;
+#endif
+
+template <int I>
+const typename relationship_t<I>::fork_t
+relationship_t<I>::fork;
+
+template <int I>
+const typename relationship_t<I>::continuation_t
+relationship_t<I>::continuation;
+
+namespace relationship {
+
+template <int I = 0>
+struct fork_t
+{
+#if defined(ASIO_HAS_VARIABLE_TEMPLATES)
+  template <typename T>
+  ASIO_STATIC_CONSTEXPR(bool,
+    is_applicable_property_v = (
+      is_executor<T>::value
+        || conditional<
+            is_executor<T>::value,
+            false_type,
+            is_sender<T>
+          >::type::value
+        || conditional<
+            is_executor<T>::value,
+            false_type,
+            is_scheduler<T>
+          >::type::value));
+#endif // defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+  ASIO_STATIC_CONSTEXPR(bool, is_requirable = true);
+  ASIO_STATIC_CONSTEXPR(bool, is_preferable = true);
+  typedef relationship_t<I> polymorphic_query_result_type;
+
+  ASIO_CONSTEXPR fork_t()
+  {
+  }
+
+  template <typename T>
+  struct query_member :
+    traits::query_member<
+      typename relationship_t<I>::template proxy<T>::type, fork_t> {};
+
+  template <typename T>
+  struct query_static_constexpr_member :
+    traits::query_static_constexpr_member<
+      typename relationship_t<I>::template static_proxy<T>::type, fork_t> {};
+
+#if defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+  template <typename T>
+  static ASIO_CONSTEXPR
+  typename query_static_constexpr_member<T>::result_type
+  static_query()
+    ASIO_NOEXCEPT_IF((
+      query_static_constexpr_member<T>::is_noexcept))
+  {
+    return query_static_constexpr_member<T>::value();
+  }
+
+  template <typename T>
+  static ASIO_CONSTEXPR fork_t static_query(
+      typename enable_if<
+        !query_static_constexpr_member<T>::is_valid
+      >::type* = 0,
+      typename enable_if<
+        !query_member<T>::is_valid
+      >::type* = 0,
+      typename enable_if<
+        !traits::query_free<T, fork_t>::is_valid
+      >::type* = 0,
+      typename enable_if<
+        !can_query<T, continuation_t<I> >::value
+      >::type* = 0) ASIO_NOEXCEPT
+  {
+    return fork_t();
+  }
+
+  template <typename E, typename T = decltype(fork_t::static_query<E>())>
+  static ASIO_CONSTEXPR const T static_query_v
+    = fork_t::static_query<E>();
+#endif // defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+  static ASIO_CONSTEXPR relationship_t<I> value()
+  {
+    return fork_t();
+  }
+
+  friend ASIO_CONSTEXPR bool operator==(
+      const fork_t&, const fork_t&)
+  {
+    return true;
+  }
+
+  friend ASIO_CONSTEXPR bool operator!=(
+      const fork_t&, const fork_t&)
+  {
+    return false;
+  }
+};
+
+#if defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+template <int I> template <typename E, typename T>
+const T fork_t<I>::static_query_v;
+#endif // defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+template <int I = 0>
+struct continuation_t
+{
+#if defined(ASIO_HAS_VARIABLE_TEMPLATES)
+  template <typename T>
+  ASIO_STATIC_CONSTEXPR(bool,
+    is_applicable_property_v = (
+      is_executor<T>::value
+        || conditional<
+            is_executor<T>::value,
+            false_type,
+            is_sender<T>
+          >::type::value
+        || conditional<
+            is_executor<T>::value,
+            false_type,
+            is_scheduler<T>
+          >::type::value));
+#endif // defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+  ASIO_STATIC_CONSTEXPR(bool, is_requirable = true);
+  ASIO_STATIC_CONSTEXPR(bool, is_preferable = true);
+  typedef relationship_t<I> polymorphic_query_result_type;
+
+  ASIO_CONSTEXPR continuation_t()
+  {
+  }
+
+  template <typename T>
+  struct query_member :
+    traits::query_member<
+      typename relationship_t<I>::template proxy<T>::type, continuation_t> {};
+
+  template <typename T>
+  struct query_static_constexpr_member :
+    traits::query_static_constexpr_member<
+      typename relationship_t<I>::template static_proxy<T>::type,
+        continuation_t> {};
+
+#if defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+  template <typename T>
+  static ASIO_CONSTEXPR
+  typename query_static_constexpr_member<T>::result_type
+  static_query()
+    ASIO_NOEXCEPT_IF((
+      query_static_constexpr_member<T>::is_noexcept))
+  {
+    return query_static_constexpr_member<T>::value();
+  }
+
+  template <typename E,
+      typename T = decltype(continuation_t::static_query<E>())>
+  static ASIO_CONSTEXPR const T static_query_v
+    = continuation_t::static_query<E>();
+#endif // defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+  static ASIO_CONSTEXPR relationship_t<I> value()
+  {
+    return continuation_t();
+  }
+
+  friend ASIO_CONSTEXPR bool operator==(
+      const continuation_t&, const continuation_t&)
+  {
+    return true;
+  }
+
+  friend ASIO_CONSTEXPR bool operator!=(
+      const continuation_t&, const continuation_t&)
+  {
+    return false;
+  }
+};
+
+#if defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+template <int I> template <typename E, typename T>
+const T continuation_t<I>::static_query_v;
+#endif // defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+} // namespace relationship
+} // namespace detail
+
+typedef detail::relationship_t<> relationship_t;
+
+#if defined(ASIO_HAS_CONSTEXPR) || defined(GENERATING_DOCUMENTATION)
+constexpr relationship_t relationship;
+#else // defined(ASIO_HAS_CONSTEXPR) || defined(GENERATING_DOCUMENTATION)
+namespace { static const relationship_t&
+  relationship = relationship_t::instance; }
+#endif
+
+} // namespace execution
+
+#if !defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename T>
+struct is_applicable_property<T, execution::relationship_t>
+  : integral_constant<bool,
+      execution::is_executor<T>::value
+        || conditional<
+            execution::is_executor<T>::value,
+            false_type,
+            execution::is_sender<T>
+          >::type::value
+        || conditional<
+            execution::is_executor<T>::value,
+            false_type,
+            execution::is_scheduler<T>
+          >::type::value>
+{
+};
+
+template <typename T>
+struct is_applicable_property<T, execution::relationship_t::fork_t>
+  : integral_constant<bool,
+      execution::is_executor<T>::value
+        || conditional<
+            execution::is_executor<T>::value,
+            false_type,
+            execution::is_sender<T>
+          >::type::value
+        || conditional<
+            execution::is_executor<T>::value,
+            false_type,
+            execution::is_scheduler<T>
+          >::type::value>
+{
+};
+
+template <typename T>
+struct is_applicable_property<T, execution::relationship_t::continuation_t>
+  : integral_constant<bool,
+      execution::is_executor<T>::value
+        || conditional<
+            execution::is_executor<T>::value,
+            false_type,
+            execution::is_sender<T>
+          >::type::value
+        || conditional<
+            execution::is_executor<T>::value,
+            false_type,
+            execution::is_scheduler<T>
+          >::type::value>
+{
+};
+
+#endif // !defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+namespace traits {
+
+#if !defined(ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+template <typename T>
+struct query_free_default<T, execution::relationship_t,
+  typename enable_if<
+    can_query<T, execution::relationship_t::fork_t>::value
+  >::type>
+{
+  ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept =
+    (is_nothrow_query<T, execution::relationship_t::fork_t>::value));
+
+  typedef execution::relationship_t result_type;
+};
+
+template <typename T>
+struct query_free_default<T, execution::relationship_t,
+  typename enable_if<
+    !can_query<T, execution::relationship_t::fork_t>::value
+      && can_query<T, execution::relationship_t::continuation_t>::value
+  >::type>
+{
+  ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept =
+    (is_nothrow_query<T, execution::relationship_t::continuation_t>::value));
+
+  typedef execution::relationship_t result_type;
+};
+
+#endif // !defined(ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
+
+#if !defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
+  || !defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+template <typename T>
+struct static_query<T, execution::relationship_t,
+  typename enable_if<
+    execution::detail::relationship_t<0>::
+      query_static_constexpr_member<T>::is_valid
+  >::type>
+{
+  ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename execution::detail::relationship_t<0>::
+    query_static_constexpr_member<T>::result_type result_type;
+
+  static ASIO_CONSTEXPR result_type value()
+  {
+    return execution::detail::relationship_t<0>::
+      query_static_constexpr_member<T>::value();
+  }
+};
+
+template <typename T>
+struct static_query<T, execution::relationship_t,
+  typename enable_if<
+    !execution::detail::relationship_t<0>::
+        query_static_constexpr_member<T>::is_valid
+      && !execution::detail::relationship_t<0>::
+        query_member<T>::is_valid
+      && traits::static_query<T,
+        execution::relationship_t::fork_t>::is_valid
+  >::type>
+{
+  ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename traits::static_query<T,
+    execution::relationship_t::fork_t>::result_type result_type;
+
+  static ASIO_CONSTEXPR result_type value()
+  {
+    return traits::static_query<T,
+        execution::relationship_t::fork_t>::value();
+  }
+};
+
+template <typename T>
+struct static_query<T, execution::relationship_t,
+  typename enable_if<
+    !execution::detail::relationship_t<0>::
+        query_static_constexpr_member<T>::is_valid
+      && !execution::detail::relationship_t<0>::
+        query_member<T>::is_valid
+      && !traits::static_query<T,
+        execution::relationship_t::fork_t>::is_valid
+      && traits::static_query<T,
+        execution::relationship_t::continuation_t>::is_valid
+  >::type>
+{
+  ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename traits::static_query<T,
+    execution::relationship_t::continuation_t>::result_type result_type;
+
+  static ASIO_CONSTEXPR result_type value()
+  {
+    return traits::static_query<T,
+        execution::relationship_t::continuation_t>::value();
+  }
+};
+
+template <typename T>
+struct static_query<T, execution::relationship_t::fork_t,
+  typename enable_if<
+    execution::detail::relationship::fork_t<0>::
+      query_static_constexpr_member<T>::is_valid
+  >::type>
+{
+  ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename execution::detail::relationship::fork_t<0>::
+    query_static_constexpr_member<T>::result_type result_type;
+
+  static ASIO_CONSTEXPR result_type value()
+  {
+    return execution::detail::relationship::fork_t<0>::
+      query_static_constexpr_member<T>::value();
+  }
+};
+
+template <typename T>
+struct static_query<T, execution::relationship_t::fork_t,
+  typename enable_if<
+    !execution::detail::relationship::fork_t<0>::
+        query_static_constexpr_member<T>::is_valid
+      && !execution::detail::relationship::fork_t<0>::
+        query_member<T>::is_valid
+      && !traits::query_free<T,
+        execution::relationship_t::fork_t>::is_valid
+      && !can_query<T, execution::relationship_t::continuation_t>::value
+  >::type>
+{
+  ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef execution::relationship_t::fork_t result_type;
+
+  static ASIO_CONSTEXPR result_type value()
+  {
+    return result_type();
+  }
+};
+
+template <typename T>
+struct static_query<T, execution::relationship_t::continuation_t,
+  typename enable_if<
+    execution::detail::relationship::continuation_t<0>::
+      query_static_constexpr_member<T>::is_valid
+  >::type>
+{
+  ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+  typedef typename execution::detail::relationship::continuation_t<0>::
+    query_static_constexpr_member<T>::result_type result_type;
+
+  static ASIO_CONSTEXPR result_type value()
+  {
+    return execution::detail::relationship::continuation_t<0>::
+      query_static_constexpr_member<T>::value();
+  }
+};
+
+#endif // !defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
+       //   || !defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
+
+#if !defined(ASIO_HAS_DEDUCED_STATIC_REQUIRE_TRAIT)
+
+template <typename T>
+struct static_require<T, execution::relationship_t::fork_t,
+  typename enable_if<
+    static_query<T, execution::relationship_t::fork_t>::is_valid
+  >::type>
+{
+  ASIO_STATIC_CONSTEXPR(bool, is_valid =
+    (is_same<typename static_query<T,
+      execution::relationship_t::fork_t>::result_type,
+        execution::relationship_t::fork_t>::value));
+};
+
+template <typename T>
+struct static_require<T, execution::relationship_t::continuation_t,
+  typename enable_if<
+    static_query<T, execution::relationship_t::continuation_t>::is_valid
+  >::type>
+{
+  ASIO_STATIC_CONSTEXPR(bool, is_valid =
+    (is_same<typename static_query<T,
+      execution::relationship_t::continuation_t>::result_type,
+        execution::relationship_t::continuation_t>::value));
+};
+
+#endif // !defined(ASIO_HAS_DEDUCED_STATIC_REQUIRE_TRAIT)
+
+} // namespace traits
+
+#endif // defined(GENERATING_DOCUMENTATION)
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_EXECUTION_RELATIONSHIP_HPP

extern/asio-1.18.2/include/asio/execution/schedule.hpp

@@ -0,0 +1,287 @@
+//
+// execution/schedule.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2021 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_EXECUTION_SCHEDULE_HPP
+#define ASIO_EXECUTION_SCHEDULE_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/detail/type_traits.hpp"
+#include "asio/execution/executor.hpp"
+#include "asio/traits/schedule_member.hpp"
+#include "asio/traits/schedule_free.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+#if defined(GENERATING_DOCUMENTATION)
+
+namespace asio {
+namespace execution {
+
+/// A customisation point that is used to obtain a sender from a scheduler.
+/**
+ * The name <tt>execution::schedule</tt> denotes a customisation point object.
+ * For some subexpression <tt>s</tt>, let <tt>S</tt> be a type such that
+ * <tt>decltype((s))</tt> is <tt>S</tt>. The expression
+ * <tt>execution::schedule(s)</tt> is expression-equivalent to:
+ *
+ * @li <tt>s.schedule()</tt>, if that expression is valid and its type models
+ *   <tt>sender</tt>.
+ *
+ * @li Otherwise, <tt>schedule(s)</tt>, if that expression is valid and its
+ *   type models <tt>sender</tt> with overload resolution performed in a context
+ *   that includes the declaration <tt>void schedule();</tt> and that does not
+ *   include a declaration of <tt>execution::schedule</tt>.
+ *
+ * @li Otherwise, <tt>S</tt> if <tt>S</tt> satisfies <tt>executor</tt>.
+ *
+ * @li Otherwise, <tt>execution::schedule(s)</tt> is ill-formed.
+ */
+inline constexpr unspecified schedule = unspecified;
+
+/// A type trait that determines whether a @c schedule expression is
+/// well-formed.
+/**
+ * Class template @c can_schedule is a trait that is derived from @c true_type
+ * if the expression <tt>execution::schedule(std::declval<S>())</tt> is well
+ * formed; otherwise @c false_type.
+ */
+template <typename S>
+struct can_schedule :
+  integral_constant<bool, automatically_determined>
+{
+};
+
+} // namespace execution
+} // namespace asio
+
+#else // defined(GENERATING_DOCUMENTATION)
+
+namespace asio_execution_schedule_fn {
+
+using asio::decay;
+using asio::declval;
+using asio::enable_if;
+using asio::execution::is_executor;
+using asio::traits::schedule_free;
+using asio::traits::schedule_member;
+
+void schedule();
+
+enum overload_type
+{
+  identity,
+  call_member,
+  call_free,
+  ill_formed
+};
+
+template <typename S, typename = void, typename = void, typename = void>
+struct call_traits
+{
+  ASIO_STATIC_CONSTEXPR(overload_type, overload = ill_formed);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef void result_type;
+};
+
+template <typename S>
+struct call_traits<S,
+  typename enable_if<
+    schedule_member<S>::is_valid
+  >::type> :
+  schedule_member<S>
+{
+  ASIO_STATIC_CONSTEXPR(overload_type, overload = call_member);
+};
+
+template <typename S>
+struct call_traits<S,
+  typename enable_if<
+    !schedule_member<S>::is_valid
+  >::type,
+  typename enable_if<
+    schedule_free<S>::is_valid
+  >::type> :
+  schedule_free<S>
+{
+  ASIO_STATIC_CONSTEXPR(overload_type, overload = call_free);
+};
+
+template <typename S>
+struct call_traits<S,
+  typename enable_if<
+    !schedule_member<S>::is_valid
+  >::type,
+  typename enable_if<
+    !schedule_free<S>::is_valid
+  >::type,
+  typename enable_if<
+    is_executor<typename decay<S>::type>::value
+  >::type>
+{
+  ASIO_STATIC_CONSTEXPR(overload_type, overload = identity);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);
+
+#if defined(ASIO_HAS_MOVE)
+  typedef ASIO_MOVE_ARG(S) result_type;
+#else // defined(ASIO_HAS_MOVE)
+  typedef ASIO_MOVE_ARG(typename decay<S>::type) result_type;
+#endif // defined(ASIO_HAS_MOVE)
+};
+
+struct impl
+{
+  template <typename S>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<S>::overload == identity,
+    typename call_traits<S>::result_type
+  >::type
+  operator()(ASIO_MOVE_ARG(S) s) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<S>::is_noexcept))
+  {
+    return ASIO_MOVE_CAST(S)(s);
+  }
+
+#if defined(ASIO_HAS_MOVE)
+  template <typename S>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<S>::overload == call_member,
+    typename call_traits<S>::result_type
+  >::type
+  operator()(S&& s) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<S>::is_noexcept))
+  {
+    return ASIO_MOVE_CAST(S)(s).schedule();
+  }
+
+  template <typename S>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<S>::overload == call_free,
+    typename call_traits<S>::result_type
+  >::type
+  operator()(S&& s) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<S>::is_noexcept))
+  {
+    return schedule(ASIO_MOVE_CAST(S)(s));
+  }
+#else // defined(ASIO_HAS_MOVE)
+  template <typename S>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<S&>::overload == call_member,
+    typename call_traits<S&>::result_type
+  >::type
+  operator()(S& s) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<S&>::is_noexcept))
+  {
+    return s.schedule();
+  }
+
+  template <typename S>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<const S&>::overload == call_member,
+    typename call_traits<const S&>::result_type
+  >::type
+  operator()(const S& s) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<const S&>::is_noexcept))
+  {
+    return s.schedule();
+  }
+
+  template <typename S>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<S&>::overload == call_free,
+    typename call_traits<S&>::result_type
+  >::type
+  operator()(S& s) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<S&>::is_noexcept))
+  {
+    return schedule(s);
+  }
+
+  template <typename S>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<const S&>::overload == call_free,
+    typename call_traits<const S&>::result_type
+  >::type
+  operator()(const S& s) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<const S&>::is_noexcept))
+  {
+    return schedule(s);
+  }
+#endif // defined(ASIO_HAS_MOVE)
+};
+
+template <typename T = impl>
+struct static_instance
+{
+  static const T instance;
+};
+
+template <typename T>
+const T static_instance<T>::instance = {};
+
+} // namespace asio_execution_schedule_fn
+namespace asio {
+namespace execution {
+namespace {
+
+static ASIO_CONSTEXPR const asio_execution_schedule_fn::impl&
+  schedule = asio_execution_schedule_fn::static_instance<>::instance;
+
+} // namespace
+
+template <typename S>
+struct can_schedule :
+  integral_constant<bool,
+    asio_execution_schedule_fn::call_traits<S>::overload !=
+      asio_execution_schedule_fn::ill_formed>
+{
+};
+
+#if defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename S>
+constexpr bool can_schedule_v = can_schedule<S>::value;
+
+#endif // defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename S>
+struct is_nothrow_schedule :
+  integral_constant<bool,
+    asio_execution_schedule_fn::call_traits<S>::is_noexcept>
+{
+};
+
+#if defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename S>
+constexpr bool is_nothrow_schedule_v
+  = is_nothrow_schedule<S>::value;
+
+#endif // defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+} // namespace execution
+} // namespace asio
+
+#endif // defined(GENERATING_DOCUMENTATION)
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_EXECUTION_SCHEDULE_HPP

extern/asio-1.18.2/include/asio/execution/scheduler.hpp

@@ -0,0 +1,86 @@
+//
+// execution/scheduler.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2021 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_EXECUTION_SCHEDULER_HPP
+#define ASIO_EXECUTION_SCHEDULER_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/detail/type_traits.hpp"
+#include "asio/execution/schedule.hpp"
+#include "asio/traits/equality_comparable.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace execution {
+namespace detail {
+
+template <typename T>
+struct is_scheduler_base :
+  integral_constant<bool,
+    is_copy_constructible<typename remove_cvref<T>::type>::value
+      && traits::equality_comparable<typename remove_cvref<T>::type>::is_valid
+  >
+{
+};
+
+} // namespace detail
+
+/// The is_scheduler trait detects whether a type T satisfies the
+/// execution::scheduler concept.
+/**
+ * Class template @c is_scheduler is a type trait that is derived from @c
+ * true_type if the type @c T meets the concept definition for a scheduler for
+ * error type @c E, otherwise @c false_type.
+ */
+template <typename T>
+struct is_scheduler :
+#if defined(GENERATING_DOCUMENTATION)
+  integral_constant<bool, automatically_determined>
+#else // defined(GENERATING_DOCUMENTATION)
+  conditional<
+    can_schedule<T>::value,
+    detail::is_scheduler_base<T>,
+    false_type
+  >::type
+#endif // defined(GENERATING_DOCUMENTATION)
+{
+};
+
+#if defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename T>
+ASIO_CONSTEXPR const bool is_scheduler_v = is_scheduler<T>::value;
+
+#endif // defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+#if defined(ASIO_HAS_CONCEPTS)
+
+template <typename T>
+ASIO_CONCEPT scheduler = is_scheduler<T>::value;
+
+#define ASIO_EXECUTION_SCHEDULER ::asio::execution::scheduler
+
+#else // defined(ASIO_HAS_CONCEPTS)
+
+#define ASIO_EXECUTION_SCHEDULER typename
+
+#endif // defined(ASIO_HAS_CONCEPTS)
+
+} // namespace execution
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_EXECUTION_SCHEDULER_HPP

extern/asio-1.18.2/include/asio/execution/sender.hpp

@@ -0,0 +1,311 @@
+//
+// execution/sender.hpp
+// ~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2021 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_EXECUTION_SENDER_HPP
+#define ASIO_EXECUTION_SENDER_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/detail/type_traits.hpp"
+#include "asio/execution/detail/as_invocable.hpp"
+#include "asio/execution/detail/void_receiver.hpp"
+#include "asio/execution/executor.hpp"
+#include "asio/execution/receiver.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+#if defined(ASIO_HAS_ALIAS_TEMPLATES) \
+  && defined(ASIO_HAS_VARIADIC_TEMPLATES) \
+  && defined(ASIO_HAS_DECLTYPE) \
+  && !defined(ASIO_MSVC) || (_MSC_VER >= 1910)
+# define ASIO_HAS_DEDUCED_EXECUTION_IS_TYPED_SENDER_TRAIT 1
+#endif // defined(ASIO_HAS_ALIAS_TEMPLATES)
+       //   && defined(ASIO_HAS_VARIADIC_TEMPLATES)
+       //   && defined(ASIO_HAS_DECLTYPE)
+       //   && !defined(ASIO_MSVC) || (_MSC_VER >= 1910)
+
+namespace asio {
+namespace execution {
+namespace detail {
+
+namespace sender_base_ns { struct sender_base {}; }
+
+template <typename S, typename = void>
+struct sender_traits_base
+{
+  typedef void asio_execution_sender_traits_base_is_unspecialised;
+};
+
+template <typename S>
+struct sender_traits_base<S,
+    typename enable_if<
+      is_base_of<sender_base_ns::sender_base, S>::value
+    >::type>
+{
+};
+
+template <typename S, typename = void, typename = void, typename = void>
+struct has_sender_types : false_type
+{
+};
+
+#if defined(ASIO_HAS_DEDUCED_EXECUTION_IS_TYPED_SENDER_TRAIT)
+
+template <
+    template <
+      template <typename...> class Tuple,
+      template <typename...> class Variant
+    > class>
+struct has_value_types
+{
+  typedef void type;
+};
+
+template <
+  template <
+    template <typename...> class Variant
+  > class>
+struct has_error_types
+{
+  typedef void type;
+};
+
+template <typename S>
+struct has_sender_types<S,
+    typename has_value_types<S::template value_types>::type,
+    typename has_error_types<S::template error_types>::type,
+    typename conditional<S::sends_done, void, void>::type> : true_type
+{
+};
+
+template <typename S>
+struct sender_traits_base<S,
+    typename enable_if<
+      has_sender_types<S>::value
+    >::type>
+{
+  template <
+      template <typename...> class Tuple,
+      template <typename...> class Variant>
+  using value_types = typename S::template value_types<Tuple, Variant>;
+
+  template <template <typename...> class Variant>
+  using error_types = typename S::template error_types<Variant>;
+
+  ASIO_STATIC_CONSTEXPR(bool, sends_done = S::sends_done);
+};
+
+#endif // defined(ASIO_HAS_DEDUCED_EXECUTION_IS_TYPED_SENDER_TRAIT)
+
+template <typename S>
+struct sender_traits_base<S,
+    typename enable_if<
+      !has_sender_types<S>::value
+        && detail::is_executor_of_impl<S,
+          as_invocable<void_receiver, S> >::value
+    >::type>
+{
+#if defined(ASIO_HAS_DEDUCED_EXECUTION_IS_TYPED_SENDER_TRAIT) \
+  && defined(ASIO_HAS_STD_EXCEPTION_PTR)
+
+  template <
+      template <typename...> class Tuple,
+      template <typename...> class Variant>
+  using value_types = Variant<Tuple<>>;
+
+  template <template <typename...> class Variant>
+  using error_types = Variant<std::exception_ptr>;
+
+  ASIO_STATIC_CONSTEXPR(bool, sends_done = true);
+
+#endif // defined(ASIO_HAS_DEDUCED_EXECUTION_IS_TYPED_SENDER_TRAIT)
+       //   && defined(ASIO_HAS_STD_EXCEPTION_PTR)
+};
+
+} // namespace detail
+
+/// Base class used for tagging senders.
+#if defined(GENERATING_DOCUMENTATION)
+typedef unspecified sender_base;
+#else // defined(GENERATING_DOCUMENTATION)
+typedef detail::sender_base_ns::sender_base sender_base;
+#endif // defined(GENERATING_DOCUMENTATION)
+
+/// Traits for senders.
+template <typename S>
+struct sender_traits
+#if !defined(GENERATING_DOCUMENTATION)
+  : detail::sender_traits_base<S>
+#endif // !defined(GENERATING_DOCUMENTATION)
+{
+};
+
+namespace detail {
+
+template <typename S, typename = void>
+struct has_sender_traits : true_type
+{
+};
+
+template <typename S>
+struct has_sender_traits<S,
+    typename enable_if<
+      is_same<
+        typename asio::execution::sender_traits<
+          S>::asio_execution_sender_traits_base_is_unspecialised,
+        void
+      >::value
+    >::type> : false_type
+{
+};
+
+} // namespace detail
+
+/// The is_sender trait detects whether a type T satisfies the
+/// execution::sender concept.
+
+/**
+ * Class template @c is_sender is a type trait that is derived from @c
+ * true_type if the type @c T meets the concept definition for a sender,
+ * otherwise @c false_type.
+ */
+template <typename T>
+struct is_sender :
+#if defined(GENERATING_DOCUMENTATION)
+  integral_constant<bool, automatically_determined>
+#else // defined(GENERATING_DOCUMENTATION)
+  conditional<
+    detail::has_sender_traits<typename remove_cvref<T>::type>::value,
+    is_move_constructible<typename remove_cvref<T>::type>,
+    false_type
+  >::type
+#endif // defined(GENERATING_DOCUMENTATION)
+{
+};
+
+#if defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename T>
+ASIO_CONSTEXPR const bool is_sender_v = is_sender<T>::value;
+
+#endif // defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+#if defined(ASIO_HAS_CONCEPTS)
+
+template <typename T>
+ASIO_CONCEPT sender = is_sender<T>::value;
+
+#define ASIO_EXECUTION_SENDER ::asio::execution::sender
+
+#else // defined(ASIO_HAS_CONCEPTS)
+
+#define ASIO_EXECUTION_SENDER typename
+
+#endif // defined(ASIO_HAS_CONCEPTS)
+
+template <typename S, typename R>
+struct can_connect;
+
+/// The is_sender_to trait detects whether a type T satisfies the
+/// execution::sender_to concept for some receiver.
+/**
+ * Class template @c is_sender_to is a type trait that is derived from @c
+ * true_type if the type @c T meets the concept definition for a sender
+ * for some receiver type R, otherwise @c false.
+ */
+template <typename T, typename R>
+struct is_sender_to :
+#if defined(GENERATING_DOCUMENTATION)
+  integral_constant<bool, automatically_determined>
+#else // defined(GENERATING_DOCUMENTATION)
+  integral_constant<bool,
+    is_sender<T>::value
+      && is_receiver<R>::value
+      && can_connect<T, R>::value
+  >
+#endif // defined(GENERATING_DOCUMENTATION)
+{
+};
+
+#if defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename T, typename R>
+ASIO_CONSTEXPR const bool is_sender_to_v =
+  is_sender_to<T, R>::value;
+
+#endif // defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+#if defined(ASIO_HAS_CONCEPTS)
+
+template <typename T, typename R>
+ASIO_CONCEPT sender_to = is_sender_to<T, R>::value;
+
+#define ASIO_EXECUTION_SENDER_TO(r) \
+  ::asio::execution::sender_to<r>
+
+#else // defined(ASIO_HAS_CONCEPTS)
+
+#define ASIO_EXECUTION_SENDER_TO(r) typename
+
+#endif // defined(ASIO_HAS_CONCEPTS)
+
+/// The is_typed_sender trait detects whether a type T satisfies the
+/// execution::typed_sender concept.
+/**
+ * Class template @c is_typed_sender is a type trait that is derived from @c
+ * true_type if the type @c T meets the concept definition for a typed sender,
+ * otherwise @c false.
+ */
+template <typename T>
+struct is_typed_sender :
+#if defined(GENERATING_DOCUMENTATION)
+  integral_constant<bool, automatically_determined>
+#else // defined(GENERATING_DOCUMENTATION)
+  integral_constant<bool,
+    is_sender<T>::value
+      && detail::has_sender_types<
+        sender_traits<typename remove_cvref<T>::type> >::value
+  >
+#endif // defined(GENERATING_DOCUMENTATION)
+{
+};
+
+#if defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename T>
+ASIO_CONSTEXPR const bool is_typed_sender_v = is_typed_sender<T>::value;
+
+#endif // defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+#if defined(ASIO_HAS_CONCEPTS)
+
+template <typename T>
+ASIO_CONCEPT typed_sender = is_typed_sender<T>::value;
+
+#define ASIO_EXECUTION_TYPED_SENDER \
+  ::asio::execution::typed_sender
+
+#else // defined(ASIO_HAS_CONCEPTS)
+
+#define ASIO_EXECUTION_TYPED_SENDER typename
+
+#endif // defined(ASIO_HAS_CONCEPTS)
+
+} // namespace execution
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#include "asio/execution/connect.hpp"
+
+#endif // ASIO_EXECUTION_SENDER_HPP

extern/asio-1.18.2/include/asio/execution/set_done.hpp

@@ -0,0 +1,250 @@
+//
+// execution/set_done.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2021 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_EXECUTION_SET_DONE_HPP
+#define ASIO_EXECUTION_SET_DONE_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/detail/type_traits.hpp"
+#include "asio/traits/set_done_member.hpp"
+#include "asio/traits/set_done_free.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+#if defined(GENERATING_DOCUMENTATION)
+
+namespace asio {
+namespace execution {
+
+/// A customisation point that delivers a done notification to a receiver.
+/**
+ * The name <tt>execution::set_done</tt> denotes a customisation point object.
+ * The expression <tt>execution::set_done(R)</tt> for some subexpression
+ * <tt>R</tt> is expression-equivalent to:
+ *
+ * @li <tt>R.set_done()</tt>, if that expression is valid. If the function
+ *   selected does not signal the receiver <tt>R</tt>'s done channel, the
+ *   program is ill-formed with no diagnostic required.
+ *
+ * @li Otherwise, <tt>set_done(R)</tt>, if that expression is valid, with
+ * overload resolution performed in a context that includes the declaration
+ * <tt>void set_done();</tt> and that does not include a declaration of
+ * <tt>execution::set_done</tt>. If the function selected by overload
+ * resolution does not signal the receiver <tt>R</tt>'s done channel, the
+ * program is ill-formed with no diagnostic required.
+ *
+ * @li Otherwise, <tt>execution::set_done(R)</tt> is ill-formed.
+ */
+inline constexpr unspecified set_done = unspecified;
+
+/// A type trait that determines whether a @c set_done expression is
+/// well-formed.
+/**
+ * Class template @c can_set_done is a trait that is derived from
+ * @c true_type if the expression <tt>execution::set_done(std::declval<R>(),
+ * std::declval<E>())</tt> is well formed; otherwise @c false_type.
+ */
+template <typename R>
+struct can_set_done :
+  integral_constant<bool, automatically_determined>
+{
+};
+
+} // namespace execution
+} // namespace asio
+
+#else // defined(GENERATING_DOCUMENTATION)
+
+namespace asio_execution_set_done_fn {
+
+using asio::decay;
+using asio::declval;
+using asio::enable_if;
+using asio::traits::set_done_free;
+using asio::traits::set_done_member;
+
+void set_done();
+
+enum overload_type
+{
+  call_member,
+  call_free,
+  ill_formed
+};
+
+template <typename R, typename = void, typename = void>
+struct call_traits
+{
+  ASIO_STATIC_CONSTEXPR(overload_type, overload = ill_formed);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef void result_type;
+};
+
+template <typename R>
+struct call_traits<R,
+  typename enable_if<
+    set_done_member<R>::is_valid
+  >::type> :
+  set_done_member<R>
+{
+  ASIO_STATIC_CONSTEXPR(overload_type, overload = call_member);
+};
+
+template <typename R>
+struct call_traits<R,
+  typename enable_if<
+    !set_done_member<R>::is_valid
+  >::type,
+  typename enable_if<
+    set_done_free<R>::is_valid
+  >::type> :
+  set_done_free<R>
+{
+  ASIO_STATIC_CONSTEXPR(overload_type, overload = call_free);
+};
+
+struct impl
+{
+#if defined(ASIO_HAS_MOVE)
+  template <typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<R>::overload == call_member,
+    typename call_traits<R>::result_type
+  >::type
+  operator()(R&& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<R>::is_noexcept))
+  {
+    return ASIO_MOVE_CAST(R)(r).set_done();
+  }
+
+  template <typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<R>::overload == call_free,
+    typename call_traits<R>::result_type
+  >::type
+  operator()(R&& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<R>::is_noexcept))
+  {
+    return set_done(ASIO_MOVE_CAST(R)(r));
+  }
+#else // defined(ASIO_HAS_MOVE)
+  template <typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<R&>::overload == call_member,
+    typename call_traits<R&>::result_type
+  >::type
+  operator()(R& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<R&>::is_noexcept))
+  {
+    return r.set_done();
+  }
+
+  template <typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<const R&>::overload == call_member,
+    typename call_traits<const R&>::result_type
+  >::type
+  operator()(const R& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<const R&>::is_noexcept))
+  {
+    return r.set_done();
+  }
+
+  template <typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<R&>::overload == call_free,
+    typename call_traits<R&>::result_type
+  >::type
+  operator()(R& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<R&>::is_noexcept))
+  {
+    return set_done(r);
+  }
+
+  template <typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<const R&>::overload == call_free,
+    typename call_traits<const R&>::result_type
+  >::type
+  operator()(const R& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<const R&>::is_noexcept))
+  {
+    return set_done(r);
+  }
+#endif // defined(ASIO_HAS_MOVE)
+};
+
+template <typename T = impl>
+struct static_instance
+{
+  static const T instance;
+};
+
+template <typename T>
+const T static_instance<T>::instance = {};
+
+} // namespace asio_execution_set_done_fn
+namespace asio {
+namespace execution {
+namespace {
+
+static ASIO_CONSTEXPR const asio_execution_set_done_fn::impl&
+  set_done = asio_execution_set_done_fn::static_instance<>::instance;
+
+} // namespace
+
+template <typename R>
+struct can_set_done :
+  integral_constant<bool,
+    asio_execution_set_done_fn::call_traits<R>::overload !=
+      asio_execution_set_done_fn::ill_formed>
+{
+};
+
+#if defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename R>
+constexpr bool can_set_done_v = can_set_done<R>::value;
+
+#endif // defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename R>
+struct is_nothrow_set_done :
+  integral_constant<bool,
+    asio_execution_set_done_fn::call_traits<R>::is_noexcept>
+{
+};
+
+#if defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename R>
+constexpr bool is_nothrow_set_done_v
+  = is_nothrow_set_done<R>::value;
+
+#endif // defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+} // namespace execution
+} // namespace asio
+
+#endif // defined(GENERATING_DOCUMENTATION)
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_EXECUTION_SET_DONE_HPP

extern/asio-1.18.2/include/asio/execution/set_error.hpp

@@ -0,0 +1,250 @@
+//
+// execution/set_error.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2021 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_EXECUTION_SET_ERROR_HPP
+#define ASIO_EXECUTION_SET_ERROR_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/detail/type_traits.hpp"
+#include "asio/traits/set_error_member.hpp"
+#include "asio/traits/set_error_free.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+#if defined(GENERATING_DOCUMENTATION)
+
+namespace asio {
+namespace execution {
+
+/// A customisation point that delivers an error notification to a receiver.
+/**
+ * The name <tt>execution::set_error</tt> denotes a customisation point object.
+ * The expression <tt>execution::set_error(R, E)</tt> for some subexpressions
+ * <tt>R</tt> and <tt>E</tt> are expression-equivalent to:
+ *
+ * @li <tt>R.set_error(E)</tt>, if that expression is valid. If the function
+ *   selected does not send the error <tt>E</tt> to the receiver <tt>R</tt>'s
+ *   error channel, the program is ill-formed with no diagnostic required.
+ *
+ * @li Otherwise, <tt>set_error(R, E)</tt>, if that expression is valid, with
+ *   overload resolution performed in a context that includes the declaration
+ *   <tt>void set_error();</tt> and that does not include a declaration of
+ *   <tt>execution::set_error</tt>. If the function selected by overload
+ *   resolution does not send the error <tt>E</tt> to the receiver <tt>R</tt>'s
+ *   error channel, the program is ill-formed with no diagnostic required.
+ *
+ * @li Otherwise, <tt>execution::set_error(R, E)</tt> is ill-formed.
+ */
+inline constexpr unspecified set_error = unspecified;
+
+/// A type trait that determines whether a @c set_error expression is
+/// well-formed.
+/**
+ * Class template @c can_set_error is a trait that is derived from
+ * @c true_type if the expression <tt>execution::set_error(std::declval<R>(),
+ * std::declval<E>())</tt> is well formed; otherwise @c false_type.
+ */
+template <typename R, typename E>
+struct can_set_error :
+  integral_constant<bool, automatically_determined>
+{
+};
+
+} // namespace execution
+} // namespace asio
+
+#else // defined(GENERATING_DOCUMENTATION)
+
+namespace asio_execution_set_error_fn {
+
+using asio::decay;
+using asio::declval;
+using asio::enable_if;
+using asio::traits::set_error_free;
+using asio::traits::set_error_member;
+
+void set_error();
+
+enum overload_type
+{
+  call_member,
+  call_free,
+  ill_formed
+};
+
+template <typename R, typename E, typename = void, typename = void>
+struct call_traits
+{
+  ASIO_STATIC_CONSTEXPR(overload_type, overload = ill_formed);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef void result_type;
+};
+
+template <typename R, typename E>
+struct call_traits<R, void(E),
+  typename enable_if<
+    set_error_member<R, E>::is_valid
+  >::type> :
+  set_error_member<R, E>
+{
+  ASIO_STATIC_CONSTEXPR(overload_type, overload = call_member);
+};
+
+template <typename R, typename E>
+struct call_traits<R, void(E),
+  typename enable_if<
+    !set_error_member<R, E>::is_valid
+  >::type,
+  typename enable_if<
+    set_error_free<R, E>::is_valid
+  >::type> :
+  set_error_free<R, E>
+{
+  ASIO_STATIC_CONSTEXPR(overload_type, overload = call_free);
+};
+
+struct impl
+{
+#if defined(ASIO_HAS_MOVE)
+  template <typename R, typename E>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<R, void(E)>::overload == call_member,
+    typename call_traits<R, void(E)>::result_type
+  >::type
+  operator()(R&& r, E&& e) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<R, void(E)>::is_noexcept))
+  {
+    return ASIO_MOVE_CAST(R)(r).set_error(ASIO_MOVE_CAST(E)(e));
+  }
+
+  template <typename R, typename E>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<R, void(E)>::overload == call_free,
+    typename call_traits<R, void(E)>::result_type
+  >::type
+  operator()(R&& r, E&& e) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<R, void(E)>::is_noexcept))
+  {
+    return set_error(ASIO_MOVE_CAST(R)(r), ASIO_MOVE_CAST(E)(e));
+  }
+#else // defined(ASIO_HAS_MOVE)
+  template <typename R, typename E>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<R&, void(const E&)>::overload == call_member,
+    typename call_traits<R&, void(const E&)>::result_type
+  >::type
+  operator()(R& r, const E& e) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<R&, void(const E&)>::is_noexcept))
+  {
+    return r.set_error(e);
+  }
+
+  template <typename R, typename E>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<const R&, void(const E&)>::overload == call_member,
+    typename call_traits<const R&, void(const E&)>::result_type
+  >::type
+  operator()(const R& r, const E& e) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<const R&, void(const E&)>::is_noexcept))
+  {
+    return r.set_error(e);
+  }
+
+  template <typename R, typename E>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<R&, void(const E&)>::overload == call_free,
+    typename call_traits<R&, void(const E&)>::result_type
+  >::type
+  operator()(R& r, const E& e) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<R&, void(const E&)>::is_noexcept))
+  {
+    return set_error(r, e);
+  }
+
+  template <typename R, typename E>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<const R&, void(const E&)>::overload == call_free,
+    typename call_traits<const R&, void(const E&)>::result_type
+  >::type
+  operator()(const R& r, const E& e) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<const R&, void(const E&)>::is_noexcept))
+  {
+    return set_error(r, e);
+  }
+#endif // defined(ASIO_HAS_MOVE)
+};
+
+template <typename T = impl>
+struct static_instance
+{
+  static const T instance;
+};
+
+template <typename T>
+const T static_instance<T>::instance = {};
+
+} // namespace asio_execution_set_error_fn
+namespace asio {
+namespace execution {
+namespace {
+
+static ASIO_CONSTEXPR const asio_execution_set_error_fn::impl&
+  set_error = asio_execution_set_error_fn::static_instance<>::instance;
+
+} // namespace
+
+template <typename R, typename E>
+struct can_set_error :
+  integral_constant<bool,
+    asio_execution_set_error_fn::call_traits<R, void(E)>::overload !=
+      asio_execution_set_error_fn::ill_formed>
+{
+};
+
+#if defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename R, typename E>
+constexpr bool can_set_error_v = can_set_error<R, E>::value;
+
+#endif // defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename R, typename E>
+struct is_nothrow_set_error :
+  integral_constant<bool,
+    asio_execution_set_error_fn::call_traits<R, void(E)>::is_noexcept>
+{
+};
+
+#if defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename R, typename E>
+constexpr bool is_nothrow_set_error_v
+  = is_nothrow_set_error<R, E>::value;
+
+#endif // defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+} // namespace execution
+} // namespace asio
+
+#endif // defined(GENERATING_DOCUMENTATION)
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_EXECUTION_SET_ERROR_HPP

extern/asio-1.18.2/include/asio/execution/set_value.hpp

@@ -0,0 +1,483 @@
+//
+// execution/set_value.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2021 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_EXECUTION_SET_VALUE_HPP
+#define ASIO_EXECUTION_SET_VALUE_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/detail/type_traits.hpp"
+#include "asio/detail/variadic_templates.hpp"
+#include "asio/traits/set_value_member.hpp"
+#include "asio/traits/set_value_free.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+#if defined(GENERATING_DOCUMENTATION)
+
+namespace asio {
+namespace execution {
+
+/// A customisation point that delivers a value to a receiver.
+/**
+ * The name <tt>execution::set_value</tt> denotes a customisation point object.
+ * The expression <tt>execution::set_value(R, Vs...)</tt> for some
+ * subexpressions <tt>R</tt> and <tt>Vs...</tt> is expression-equivalent to:
+ *
+ * @li <tt>R.set_value(Vs...)</tt>, if that expression is valid. If the
+ *   function selected does not send the value(s) <tt>Vs...</tt> to the receiver
+ *   <tt>R</tt>'s value channel, the program is ill-formed with no diagnostic
+ *   required.
+ *
+ * @li Otherwise, <tt>set_value(R, Vs...)</tt>, if that expression is valid,
+ *   with overload resolution performed in a context that includes the
+ *   declaration <tt>void set_value();</tt> and that does not include a
+ *   declaration of <tt>execution::set_value</tt>. If the function selected by
+ *   overload resolution does not send the value(s) <tt>Vs...</tt> to the
+ *   receiver <tt>R</tt>'s value channel, the program is ill-formed with no
+ *   diagnostic required.
+ *
+ * @li Otherwise, <tt>execution::set_value(R, Vs...)</tt> is ill-formed.
+ */
+inline constexpr unspecified set_value = unspecified;
+
+/// A type trait that determines whether a @c set_value expression is
+/// well-formed.
+/**
+ * Class template @c can_set_value is a trait that is derived from
+ * @c true_type if the expression <tt>execution::set_value(std::declval<R>(),
+ * std::declval<Vs>()...)</tt> is well formed; otherwise @c false_type.
+ */
+template <typename R, typename... Vs>
+struct can_set_value :
+  integral_constant<bool, automatically_determined>
+{
+};
+
+} // namespace execution
+} // namespace asio
+
+#else // defined(GENERATING_DOCUMENTATION)
+
+namespace asio_execution_set_value_fn {
+
+using asio::decay;
+using asio::declval;
+using asio::enable_if;
+using asio::traits::set_value_free;
+using asio::traits::set_value_member;
+
+void set_value();
+
+enum overload_type
+{
+  call_member,
+  call_free,
+  ill_formed
+};
+
+template <typename R, typename Vs, typename = void, typename = void>
+struct call_traits
+{
+  ASIO_STATIC_CONSTEXPR(overload_type, overload = ill_formed);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef void result_type;
+};
+
+template <typename R, typename Vs>
+struct call_traits<R, Vs,
+  typename enable_if<
+    set_value_member<R, Vs>::is_valid
+  >::type> :
+  set_value_member<R, Vs>
+{
+  ASIO_STATIC_CONSTEXPR(overload_type, overload = call_member);
+};
+
+template <typename R, typename Vs>
+struct call_traits<R, Vs,
+  typename enable_if<
+    !set_value_member<R, Vs>::is_valid
+  >::type,
+  typename enable_if<
+    set_value_free<R, Vs>::is_valid
+  >::type> :
+  set_value_free<R, Vs>
+{
+  ASIO_STATIC_CONSTEXPR(overload_type, overload = call_free);
+};
+
+struct impl
+{
+#if defined(ASIO_HAS_MOVE)
+
+#if defined(ASIO_HAS_VARIADIC_TEMPLATES)
+
+  template <typename R, typename... Vs>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<R, void(Vs...)>::overload == call_member,
+    typename call_traits<R, void(Vs...)>::result_type
+  >::type
+  operator()(R&& r, Vs&&... v) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<R, void(Vs...)>::is_noexcept))
+  {
+    return ASIO_MOVE_CAST(R)(r).set_value(ASIO_MOVE_CAST(Vs)(v)...);
+  }
+
+  template <typename R, typename... Vs>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<R, void(Vs...)>::overload == call_free,
+    typename call_traits<R, void(Vs...)>::result_type
+  >::type
+  operator()(R&& r, Vs&&... v) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<R, void(Vs...)>::is_noexcept))
+  {
+    return set_value(ASIO_MOVE_CAST(R)(r),
+        ASIO_MOVE_CAST(Vs)(v)...);
+  }
+
+#else // defined(ASIO_HAS_VARIADIC_TEMPLATES)
+
+  template <typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<R, void()>::overload == call_member,
+    typename call_traits<R, void()>::result_type
+  >::type
+  operator()(R&& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<R, void()>::is_noexcept))
+  {
+    return ASIO_MOVE_CAST(R)(r).set_value();
+  }
+
+  template <typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<R, void()>::overload == call_free,
+    typename call_traits<R, void()>::result_type
+  >::type
+  operator()(R&& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<R, void()>::is_noexcept))
+  {
+    return set_value(ASIO_MOVE_CAST(R)(r));
+  }
+
+#define ASIO_PRIVATE_SET_VALUE_CALL_DEF(n) \
+  template <typename R, ASIO_VARIADIC_TPARAMS(n)> \
+  ASIO_CONSTEXPR typename enable_if< \
+    call_traits<R, \
+      void(ASIO_VARIADIC_TARGS(n))>::overload == call_member, \
+    typename call_traits<R, void(ASIO_VARIADIC_TARGS(n))>::result_type \
+  >::type \
+  operator()(R&& r, ASIO_VARIADIC_MOVE_PARAMS(n)) const \
+    ASIO_NOEXCEPT_IF(( \
+      call_traits<R, void(ASIO_VARIADIC_TARGS(n))>::is_noexcept)) \
+  { \
+    return ASIO_MOVE_CAST(R)(r).set_value( \
+        ASIO_VARIADIC_MOVE_ARGS(n)); \
+  } \
+  \
+  template <typename R, ASIO_VARIADIC_TPARAMS(n)> \
+  ASIO_CONSTEXPR typename enable_if< \
+    call_traits<R, void(ASIO_VARIADIC_TARGS(n))>::overload == call_free, \
+    typename call_traits<R, void(ASIO_VARIADIC_TARGS(n))>::result_type \
+  >::type \
+  operator()(R&& r, ASIO_VARIADIC_MOVE_PARAMS(n)) const \
+    ASIO_NOEXCEPT_IF(( \
+      call_traits<R, void(ASIO_VARIADIC_TARGS(n))>::is_noexcept)) \
+  { \
+    return set_value(ASIO_MOVE_CAST(R)(r), \
+        ASIO_VARIADIC_MOVE_ARGS(n)); \
+  } \
+  /**/
+ASIO_VARIADIC_GENERATE(ASIO_PRIVATE_SET_VALUE_CALL_DEF)
+#undef ASIO_PRIVATE_SET_VALUE_CALL_DEF
+
+#endif // defined(ASIO_HAS_VARIADIC_TEMPLATES)
+
+#else // defined(ASIO_HAS_MOVE)
+
+#if defined(ASIO_HAS_VARIADIC_TEMPLATES)
+
+  template <typename R, typename... Vs>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<R&, void(const Vs&...)>::overload == call_member,
+    typename call_traits<R&, void(const Vs&...)>::result_type
+  >::type
+  operator()(R& r, const Vs&... v) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<R&, void(const Vs&...)>::is_noexcept))
+  {
+    return r.set_value(v...);
+  }
+
+  template <typename R, typename... Vs>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<const R&, void(const Vs&...)>::overload == call_member,
+    typename call_traits<const R&, void(const Vs&...)>::result_type
+  >::type
+  operator()(const R& r, const Vs&... v) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<const R&, void(const Vs&...)>::is_noexcept))
+  {
+    return r.set_value(v...);
+  }
+
+  template <typename R, typename... Vs>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<R&, void(const Vs&...)>::overload == call_free,
+    typename call_traits<R&, void(const Vs&...)>::result_type
+  >::type
+  operator()(R& r, const Vs&... v) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<R&, void(const Vs&...)>::is_noexcept))
+  {
+    return set_value(r, v...);
+  }
+
+  template <typename R, typename... Vs>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<const R&, void(const Vs&...)>::overload == call_free,
+    typename call_traits<const R&, void(const Vs&...)>::result_type
+  >::type
+  operator()(const R& r, const Vs&... v) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<const R&, void(const Vs&...)>::is_noexcept))
+  {
+    return set_value(r, v...);
+  }
+
+#else // defined(ASIO_HAS_VARIADIC_TEMPLATES)
+
+  template <typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<R&, void()>::overload == call_member,
+    typename call_traits<R&, void()>::result_type
+  >::type
+  operator()(R& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<R&, void()>::is_noexcept))
+  {
+    return r.set_value();
+  }
+
+  template <typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<const R&, void()>::overload == call_member,
+    typename call_traits<const R&, void()>::result_type
+  >::type
+  operator()(const R& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<const R&, void()>::is_noexcept))
+  {
+    return r.set_value();
+  }
+
+  template <typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<R&, void()>::overload == call_free,
+    typename call_traits<R&, void()>::result_type
+  >::type
+  operator()(R& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<R&, void()>::is_noexcept))
+  {
+    return set_value(r);
+  }
+
+  template <typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<const R&, void()>::overload == call_free,
+    typename call_traits<const R&, void()>::result_type
+  >::type
+  operator()(const R& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<const R&, void()>::is_noexcept))
+  {
+    return set_value(r);
+  }
+
+#define ASIO_PRIVATE_SET_VALUE_CALL_DEF(n) \
+  template <typename R, ASIO_VARIADIC_TPARAMS(n)> \
+  ASIO_CONSTEXPR typename enable_if< \
+    call_traits<R&, \
+      void(ASIO_VARIADIC_TARGS(n))>::overload == call_member, \
+    typename call_traits<R&, void(ASIO_VARIADIC_TARGS(n))>::result_type \
+  >::type \
+  operator()(R& r, ASIO_VARIADIC_MOVE_PARAMS(n)) const \
+    ASIO_NOEXCEPT_IF(( \
+      call_traits<R&, void(ASIO_VARIADIC_TARGS(n))>::is_noexcept)) \
+  { \
+    return r.set_value(ASIO_VARIADIC_MOVE_ARGS(n)); \
+  } \
+  \
+  template <typename R, ASIO_VARIADIC_TPARAMS(n)> \
+  ASIO_CONSTEXPR typename enable_if< \
+    call_traits<const R&, \
+      void(ASIO_VARIADIC_TARGS(n))>::overload == call_member, \
+    typename call_traits<const R&, \
+      void(ASIO_VARIADIC_TARGS(n))>::result_type \
+  >::type \
+  operator()(const R& r, ASIO_VARIADIC_MOVE_PARAMS(n)) const \
+    ASIO_NOEXCEPT_IF(( \
+      call_traits<const R&, void(ASIO_VARIADIC_TARGS(n))>::is_noexcept)) \
+  { \
+    return r.set_value(ASIO_VARIADIC_MOVE_ARGS(n)); \
+  } \
+  \
+  template <typename R, ASIO_VARIADIC_TPARAMS(n)> \
+  ASIO_CONSTEXPR typename enable_if< \
+    call_traits<R&, \
+      void(ASIO_VARIADIC_TARGS(n))>::overload == call_free, \
+    typename call_traits<R&, void(ASIO_VARIADIC_TARGS(n))>::result_type \
+  >::type \
+  operator()(R& r, ASIO_VARIADIC_MOVE_PARAMS(n)) const \
+    ASIO_NOEXCEPT_IF(( \
+      call_traits<R&, void(ASIO_VARIADIC_TARGS(n))>::is_noexcept)) \
+  { \
+    return set_value(r, ASIO_VARIADIC_MOVE_ARGS(n)); \
+  } \
+  \
+  template <typename R, ASIO_VARIADIC_TPARAMS(n)> \
+  ASIO_CONSTEXPR typename enable_if< \
+    call_traits<const R&, \
+      void(ASIO_VARIADIC_TARGS(n))>::overload == call_free, \
+    typename call_traits<const R&, \
+      void(ASIO_VARIADIC_TARGS(n))>::result_type \
+  >::type \
+  operator()(const R& r, ASIO_VARIADIC_MOVE_PARAMS(n)) const \
+    ASIO_NOEXCEPT_IF(( \
+      call_traits<const R&, void(ASIO_VARIADIC_TARGS(n))>::is_noexcept)) \
+  { \
+    return set_value(r, ASIO_VARIADIC_MOVE_ARGS(n)); \
+  } \
+  /**/
+ASIO_VARIADIC_GENERATE(ASIO_PRIVATE_SET_VALUE_CALL_DEF)
+#undef ASIO_PRIVATE_SET_VALUE_CALL_DEF
+
+#endif // defined(ASIO_HAS_VARIADIC_TEMPLATES)
+
+#endif // defined(ASIO_HAS_MOVE)
+};
+
+template <typename T = impl>
+struct static_instance
+{
+  static const T instance;
+};
+
+template <typename T>
+const T static_instance<T>::instance = {};
+
+} // namespace asio_execution_set_value_fn
+namespace asio {
+namespace execution {
+namespace {
+
+static ASIO_CONSTEXPR const asio_execution_set_value_fn::impl&
+  set_value = asio_execution_set_value_fn::static_instance<>::instance;
+
+} // namespace
+
+#if defined(ASIO_HAS_VARIADIC_TEMPLATES)
+
+template <typename R, typename... Vs>
+struct can_set_value :
+  integral_constant<bool,
+    asio_execution_set_value_fn::call_traits<R, void(Vs...)>::overload !=
+      asio_execution_set_value_fn::ill_formed>
+{
+};
+
+#if defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename R, typename... Vs>
+constexpr bool can_set_value_v = can_set_value<R, Vs...>::value;
+
+#endif // defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename R, typename... Vs>
+struct is_nothrow_set_value :
+  integral_constant<bool,
+    asio_execution_set_value_fn::call_traits<R, void(Vs...)>::is_noexcept>
+{
+};
+
+#if defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename R, typename... Vs>
+constexpr bool is_nothrow_set_value_v
+  = is_nothrow_set_value<R, Vs...>::value;
+
+#endif // defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+#else // defined(ASIO_HAS_VARIADIC_TEMPLATES)
+
+template <typename R, typename = void,
+    typename = void, typename = void, typename = void, typename = void,
+    typename = void, typename = void, typename = void, typename = void>
+struct can_set_value;
+
+template <typename R, typename = void,
+    typename = void, typename = void, typename = void, typename = void,
+    typename = void, typename = void, typename = void, typename = void>
+struct is_nothrow_set_value;
+
+template <typename R>
+struct can_set_value<R> :
+  integral_constant<bool,
+    asio_execution_set_value_fn::call_traits<R, void()>::overload !=
+      asio_execution_set_value_fn::ill_formed>
+{
+};
+
+template <typename R>
+struct is_nothrow_set_value<R> :
+  integral_constant<bool,
+    asio_execution_set_value_fn::call_traits<R, void()>::is_noexcept>
+{
+};
+
+#define ASIO_PRIVATE_SET_VALUE_TRAITS_DEF(n) \
+  template <typename R, ASIO_VARIADIC_TPARAMS(n)> \
+  struct can_set_value<R, ASIO_VARIADIC_TARGS(n)> : \
+    integral_constant<bool, \
+      asio_execution_set_value_fn::call_traits<R, \
+        void(ASIO_VARIADIC_TARGS(n))>::overload != \
+          asio_execution_set_value_fn::ill_formed> \
+  { \
+  }; \
+  \
+  template <typename R, ASIO_VARIADIC_TPARAMS(n)> \
+  struct is_nothrow_set_value<R, ASIO_VARIADIC_TARGS(n)> : \
+    integral_constant<bool, \
+      asio_execution_set_value_fn::call_traits<R, \
+        void(ASIO_VARIADIC_TARGS(n))>::is_noexcept> \
+  { \
+  }; \
+  /**/
+ASIO_VARIADIC_GENERATE(ASIO_PRIVATE_SET_VALUE_TRAITS_DEF)
+#undef ASIO_PRIVATE_SET_VALUE_TRAITS_DEF
+
+#endif // defined(ASIO_HAS_VARIADIC_TEMPLATES)
+
+} // namespace execution
+} // namespace asio
+
+#endif // defined(GENERATING_DOCUMENTATION)
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_EXECUTION_SET_VALUE_HPP

extern/asio-1.18.2/include/asio/execution/start.hpp

@@ -0,0 +1,247 @@
+//
+// execution/start.hpp
+// ~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2021 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_EXECUTION_START_HPP
+#define ASIO_EXECUTION_START_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/detail/type_traits.hpp"
+#include "asio/traits/start_member.hpp"
+#include "asio/traits/start_free.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+#if defined(GENERATING_DOCUMENTATION)
+
+namespace asio {
+namespace execution {
+
+/// A customisation point that notifies an operation state object to start
+/// its associated operation.
+/**
+ * The name <tt>execution::start</tt> denotes a customisation point object.
+ * The expression <tt>execution::start(R)</tt> for some subexpression
+ * <tt>R</tt> is expression-equivalent to:
+ *
+ * @li <tt>R.start()</tt>, if that expression is valid.
+ *
+ * @li Otherwise, <tt>start(R)</tt>, if that expression is valid, with
+ * overload resolution performed in a context that includes the declaration
+ * <tt>void start();</tt> and that does not include a declaration of
+ * <tt>execution::start</tt>.
+ *
+ * @li Otherwise, <tt>execution::start(R)</tt> is ill-formed.
+ */
+inline constexpr unspecified start = unspecified;
+
+/// A type trait that determines whether a @c start expression is
+/// well-formed.
+/**
+ * Class template @c can_start is a trait that is derived from
+ * @c true_type if the expression <tt>execution::start(std::declval<R>(),
+ * std::declval<E>())</tt> is well formed; otherwise @c false_type.
+ */
+template <typename R>
+struct can_start :
+  integral_constant<bool, automatically_determined>
+{
+};
+
+} // namespace execution
+} // namespace asio
+
+#else // defined(GENERATING_DOCUMENTATION)
+
+namespace asio_execution_start_fn {
+
+using asio::decay;
+using asio::declval;
+using asio::enable_if;
+using asio::traits::start_free;
+using asio::traits::start_member;
+
+void start();
+
+enum overload_type
+{
+  call_member,
+  call_free,
+  ill_formed
+};
+
+template <typename R, typename = void, typename = void>
+struct call_traits
+{
+  ASIO_STATIC_CONSTEXPR(overload_type, overload = ill_formed);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef void result_type;
+};
+
+template <typename R>
+struct call_traits<R,
+  typename enable_if<
+    start_member<R>::is_valid
+  >::type> :
+  start_member<R>
+{
+  ASIO_STATIC_CONSTEXPR(overload_type, overload = call_member);
+};
+
+template <typename R>
+struct call_traits<R,
+  typename enable_if<
+    !start_member<R>::is_valid
+  >::type,
+  typename enable_if<
+    start_free<R>::is_valid
+  >::type> :
+  start_free<R>
+{
+  ASIO_STATIC_CONSTEXPR(overload_type, overload = call_free);
+};
+
+struct impl
+{
+#if defined(ASIO_HAS_MOVE)
+  template <typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<R>::overload == call_member,
+    typename call_traits<R>::result_type
+  >::type
+  operator()(R&& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<R>::is_noexcept))
+  {
+    return ASIO_MOVE_CAST(R)(r).start();
+  }
+
+  template <typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<R>::overload == call_free,
+    typename call_traits<R>::result_type
+  >::type
+  operator()(R&& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<R>::is_noexcept))
+  {
+    return start(ASIO_MOVE_CAST(R)(r));
+  }
+#else // defined(ASIO_HAS_MOVE)
+  template <typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<R&>::overload == call_member,
+    typename call_traits<R&>::result_type
+  >::type
+  operator()(R& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<R&>::is_noexcept))
+  {
+    return r.start();
+  }
+
+  template <typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<const R&>::overload == call_member,
+    typename call_traits<const R&>::result_type
+  >::type
+  operator()(const R& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<const R&>::is_noexcept))
+  {
+    return r.start();
+  }
+
+  template <typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<R&>::overload == call_free,
+    typename call_traits<R&>::result_type
+  >::type
+  operator()(R& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<R&>::is_noexcept))
+  {
+    return start(r);
+  }
+
+  template <typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<const R&>::overload == call_free,
+    typename call_traits<const R&>::result_type
+  >::type
+  operator()(const R& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<const R&>::is_noexcept))
+  {
+    return start(r);
+  }
+#endif // defined(ASIO_HAS_MOVE)
+};
+
+template <typename T = impl>
+struct static_instance
+{
+  static const T instance;
+};
+
+template <typename T>
+const T static_instance<T>::instance = {};
+
+} // namespace asio_execution_start_fn
+namespace asio {
+namespace execution {
+namespace {
+
+static ASIO_CONSTEXPR const asio_execution_start_fn::impl&
+  start = asio_execution_start_fn::static_instance<>::instance;
+
+} // namespace
+
+template <typename R>
+struct can_start :
+  integral_constant<bool,
+    asio_execution_start_fn::call_traits<R>::overload !=
+      asio_execution_start_fn::ill_formed>
+{
+};
+
+#if defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename R>
+constexpr bool can_start_v = can_start<R>::value;
+
+#endif // defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename R>
+struct is_nothrow_start :
+  integral_constant<bool,
+    asio_execution_start_fn::call_traits<R>::is_noexcept>
+{
+};
+
+#if defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename R>
+constexpr bool is_nothrow_start_v
+  = is_nothrow_start<R>::value;
+
+#endif // defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+} // namespace execution
+} // namespace asio
+
+#endif // defined(GENERATING_DOCUMENTATION)
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_EXECUTION_START_HPP

extern/asio-1.18.2/include/asio/execution/submit.hpp

@@ -0,0 +1,450 @@
+//
+// execution/submit.hpp
+// ~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2021 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_EXECUTION_SUBMIT_HPP
+#define ASIO_EXECUTION_SUBMIT_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/detail/type_traits.hpp"
+#include "asio/execution/detail/submit_receiver.hpp"
+#include "asio/execution/executor.hpp"
+#include "asio/execution/receiver.hpp"
+#include "asio/execution/sender.hpp"
+#include "asio/execution/start.hpp"
+#include "asio/traits/submit_member.hpp"
+#include "asio/traits/submit_free.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+#if defined(GENERATING_DOCUMENTATION)
+
+namespace asio {
+namespace execution {
+
+/// A customisation point that submits a sender to a receiver.
+/**
+ * The name <tt>execution::submit</tt> denotes a customisation point object. For
+ * some subexpressions <tt>s</tt> and <tt>r</tt>, let <tt>S</tt> be a type such
+ * that <tt>decltype((s))</tt> is <tt>S</tt> and let <tt>R</tt> be a type such
+ * that <tt>decltype((r))</tt> is <tt>R</tt>. The expression
+ * <tt>execution::submit(s, r)</tt> is ill-formed if <tt>sender_to<S, R></tt> is
+ * not <tt>true</tt>. Otherwise, it is expression-equivalent to:
+ *
+ * @li <tt>s.submit(r)</tt>, if that expression is valid and <tt>S</tt> models
+ *   <tt>sender</tt>. If the function selected does not submit the receiver
+ *   object <tt>r</tt> via the sender <tt>s</tt>, the program is ill-formed with
+ *   no diagnostic required.
+ *
+ * @li Otherwise, <tt>submit(s, r)</tt>, if that expression is valid and
+ *   <tt>S</tt> models <tt>sender</tt>, with overload resolution performed in a
+ *   context that includes the declaration <tt>void submit();</tt> and that does
+ *   not include a declaration of <tt>execution::submit</tt>. If the function
+ *   selected by overload resolution does not submit the receiver object
+ *   <tt>r</tt> via the sender <tt>s</tt>, the program is ill-formed with no
+ *   diagnostic required.
+ *
+ * @li Otherwise, <tt>execution::start((new submit_receiver<S,
+ *   R>{s,r})->state_)</tt>, where <tt>submit_receiver</tt> is an
+ *   implementation-defined class template equivalent to:
+ *   @code template<class S, class R>
+ *   struct submit_receiver {
+ *     struct wrap {
+ *       submit_receiver * p_;
+ *       template<class...As>
+ *         requires receiver_of<R, As...>
+ *       void set_value(As&&... as) &&
+ *         noexcept(is_nothrow_receiver_of_v<R, As...>) {
+ *         execution::set_value(std::move(p_->r_), (As&&) as...);
+ *         delete p_;
+ *       }
+ *       template<class E>
+ *         requires receiver<R, E>
+ *       void set_error(E&& e) && noexcept {
+ *         execution::set_error(std::move(p_->r_), (E&&) e);
+ *         delete p_;
+ *       }
+ *       void set_done() && noexcept {
+ *         execution::set_done(std::move(p_->r_));
+ *         delete p_;
+ *       }
+ *     };
+ *     remove_cvref_t<R> r_;
+ *     connect_result_t<S, wrap> state_;
+ *     submit_receiver(S&& s, R&& r)
+ *       : r_((R&&) r)
+ *       , state_(execution::connect((S&&) s, wrap{this})) {}
+ *   };
+ *   @endcode
+ */
+inline constexpr unspecified submit = unspecified;
+
+/// A type trait that determines whether a @c submit expression is
+/// well-formed.
+/**
+ * Class template @c can_submit is a trait that is derived from
+ * @c true_type if the expression <tt>execution::submit(std::declval<R>(),
+ * std::declval<E>())</tt> is well formed; otherwise @c false_type.
+ */
+template <typename S, typename R>
+struct can_submit :
+  integral_constant<bool, automatically_determined>
+{
+};
+
+} // namespace execution
+} // namespace asio
+
+#else // defined(GENERATING_DOCUMENTATION)
+
+namespace asio_execution_submit_fn {
+
+using asio::declval;
+using asio::enable_if;
+using asio::execution::is_sender_to;
+using asio::traits::submit_free;
+using asio::traits::submit_member;
+
+void submit();
+
+enum overload_type
+{
+  call_member,
+  call_free,
+  adapter,
+  ill_formed
+};
+
+template <typename S, typename R, typename = void,
+    typename = void, typename = void>
+struct call_traits
+{
+  ASIO_STATIC_CONSTEXPR(overload_type, overload = ill_formed);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef void result_type;
+};
+
+template <typename S, typename R>
+struct call_traits<S, void(R),
+  typename enable_if<
+    submit_member<S, R>::is_valid
+  >::type,
+  typename enable_if<
+    is_sender_to<S, R>::value
+  >::type> :
+  submit_member<S, R>
+{
+  ASIO_STATIC_CONSTEXPR(overload_type, overload = call_member);
+};
+
+template <typename S, typename R>
+struct call_traits<S, void(R),
+  typename enable_if<
+    !submit_member<S, R>::is_valid
+  >::type,
+  typename enable_if<
+    submit_free<S, R>::is_valid
+  >::type,
+  typename enable_if<
+    is_sender_to<S, R>::value
+  >::type> :
+  submit_free<S, R>
+{
+  ASIO_STATIC_CONSTEXPR(overload_type, overload = call_free);
+};
+
+template <typename S, typename R>
+struct call_traits<S, void(R),
+  typename enable_if<
+    !submit_member<S, R>::is_valid
+  >::type,
+  typename enable_if<
+    !submit_free<S, R>::is_valid
+  >::type,
+  typename enable_if<
+    is_sender_to<S, R>::value
+  >::type>
+{
+  ASIO_STATIC_CONSTEXPR(overload_type, overload = adapter);
+  ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
+  typedef void result_type;
+};
+
+struct impl
+{
+#if defined(ASIO_HAS_MOVE)
+  template <typename S, typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<S, void(R)>::overload == call_member,
+    typename call_traits<S, void(R)>::result_type
+  >::type
+  operator()(S&& s, R&& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<S, void(R)>::is_noexcept))
+  {
+    return ASIO_MOVE_CAST(S)(s).submit(ASIO_MOVE_CAST(R)(r));
+  }
+
+  template <typename S, typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<S, void(R)>::overload == call_free,
+    typename call_traits<S, void(R)>::result_type
+  >::type
+  operator()(S&& s, R&& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<S, void(R)>::is_noexcept))
+  {
+    return submit(ASIO_MOVE_CAST(S)(s), ASIO_MOVE_CAST(R)(r));
+  }
+
+  template <typename S, typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<S, void(R)>::overload == adapter,
+    typename call_traits<S, void(R)>::result_type
+  >::type
+  operator()(S&& s, R&& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<S, void(R)>::is_noexcept))
+  {
+    return asio::execution::start(
+        (new asio::execution::detail::submit_receiver<S, R>(
+          ASIO_MOVE_CAST(S)(s), ASIO_MOVE_CAST(R)(r)))->state_);
+  }
+#else // defined(ASIO_HAS_MOVE)
+  template <typename S, typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<S&, void(R&)>::overload == call_member,
+    typename call_traits<S&, void(R&)>::result_type
+  >::type
+  operator()(S& s, R& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<S&, void(R&)>::is_noexcept))
+  {
+    return s.submit(r);
+  }
+
+  template <typename S, typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<const S&, void(R&)>::overload == call_member,
+    typename call_traits<const S&, void(R&)>::result_type
+  >::type
+  operator()(const S& s, R& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<const S&, void(R&)>::is_noexcept))
+  {
+    return s.submit(r);
+  }
+
+  template <typename S, typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<S&, void(R&)>::overload == call_free,
+    typename call_traits<S&, void(R&)>::result_type
+  >::type
+  operator()(S& s, R& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<S&, void(R&)>::is_noexcept))
+  {
+    return submit(s, r);
+  }
+
+  template <typename S, typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<const S&, void(R&)>::overload == call_free,
+    typename call_traits<const S&, void(R&)>::result_type
+  >::type
+  operator()(const S& s, R& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<const S&, void(R&)>::is_noexcept))
+  {
+    return submit(s, r);
+  }
+
+  template <typename S, typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<S&, void(R&)>::overload == adapter,
+    typename call_traits<S&, void(R&)>::result_type
+  >::type
+  operator()(S& s, R& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<S&, void(R&)>::is_noexcept))
+  {
+    return asio::execution::start(
+        (new asio::execution::detail::submit_receiver<
+          S&, R&>(s, r))->state_);
+  }
+
+  template <typename S, typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<const S&, void(R&)>::overload == adapter,
+    typename call_traits<const S&, void(R&)>::result_type
+  >::type
+  operator()(const S& s, R& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<const S&, void(R&)>::is_noexcept))
+  {
+    asio::execution::start(
+        (new asio::execution::detail::submit_receiver<
+          const S&, R&>(s, r))->state_);
+  }
+
+  template <typename S, typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<S&, void(const R&)>::overload == call_member,
+    typename call_traits<S&, void(const R&)>::result_type
+  >::type
+  operator()(S& s, const R& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<S&, void(const R&)>::is_noexcept))
+  {
+    return s.submit(r);
+  }
+
+  template <typename S, typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<const S&, void(const R&)>::overload == call_member,
+    typename call_traits<const S&, void(const R&)>::result_type
+  >::type
+  operator()(const S& s, const R& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<const S&, void(const R&)>::is_noexcept))
+  {
+    return s.submit(r);
+  }
+
+  template <typename S, typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<S&, void(const R&)>::overload == call_free,
+    typename call_traits<S&, void(const R&)>::result_type
+  >::type
+  operator()(S& s, const R& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<S&, void(const R&)>::is_noexcept))
+  {
+    return submit(s, r);
+  }
+
+  template <typename S, typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<const S&, void(const R&)>::overload == call_free,
+    typename call_traits<const S&, void(const R&)>::result_type
+  >::type
+  operator()(const S& s, const R& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<const S&, void(const R&)>::is_noexcept))
+  {
+    return submit(s, r);
+  }
+
+  template <typename S, typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<S&, void(const R&)>::overload == adapter,
+    typename call_traits<S&, void(const R&)>::result_type
+  >::type
+  operator()(S& s, const R& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<S&, void(const R&)>::is_noexcept))
+  {
+    asio::execution::start(
+        (new asio::execution::detail::submit_receiver<
+          S&, const R&>(s, r))->state_);
+  }
+
+  template <typename S, typename R>
+  ASIO_CONSTEXPR typename enable_if<
+    call_traits<const S&, void(const R&)>::overload == adapter,
+    typename call_traits<const S&, void(const R&)>::result_type
+  >::type
+  operator()(const S& s, const R& r) const
+    ASIO_NOEXCEPT_IF((
+      call_traits<const S&, void(const R&)>::is_noexcept))
+  {
+    asio::execution::start(
+        (new asio::execution::detail::submit_receiver<
+          const S&, const R&>(s, r))->state_);
+  }
+#endif // defined(ASIO_HAS_MOVE)
+};
+
+template <typename T = impl>
+struct static_instance
+{
+  static const T instance;
+};
+
+template <typename T>
+const T static_instance<T>::instance = {};
+
+} // namespace asio_execution_submit_fn
+namespace asio {
+namespace execution {
+namespace {
+
+static ASIO_CONSTEXPR const asio_execution_submit_fn::impl&
+  submit = asio_execution_submit_fn::static_instance<>::instance;
+
+} // namespace
+
+template <typename S, typename R>
+struct can_submit :
+  integral_constant<bool,
+    asio_execution_submit_fn::call_traits<S, void(R)>::overload !=
+      asio_execution_submit_fn::ill_formed>
+{
+};
+
+#if defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename S, typename R>
+constexpr bool can_submit_v = can_submit<S, R>::value;
+
+#endif // defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename S, typename R>
+struct is_nothrow_submit :
+  integral_constant<bool,
+    asio_execution_submit_fn::call_traits<S, void(R)>::is_noexcept>
+{
+};
+
+#if defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename S, typename R>
+constexpr bool is_nothrow_submit_v
+  = is_nothrow_submit<S, R>::value;
+
+#endif // defined(ASIO_HAS_VARIABLE_TEMPLATES)
+
+template <typename S, typename R>
+struct submit_result
+{
+  typedef typename asio_execution_submit_fn::call_traits<
+      S, void(R)>::result_type type;
+};
+
+namespace detail {
+
+template <typename S, typename R>
+void submit_helper(ASIO_MOVE_ARG(S) s, ASIO_MOVE_ARG(R) r)
+{
+  execution::submit(ASIO_MOVE_CAST(S)(s), ASIO_MOVE_CAST(R)(r));
+}
+
+} // namespace detail
+} // namespace execution
+} // namespace asio
+
+#endif // defined(GENERATING_DOCUMENTATION)
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_EXECUTION_SUBMIT_HPP