325 lines
8.8 KiB
C++
325 lines
8.8 KiB
C++
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//
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// query.hpp
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// ~~~~~~~~~
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//
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// Copyright (c) 2003-2021 Christopher M. Kohlhoff (chris at kohlhoff dot com)
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//
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// Distributed under the Boost Software License, Version 1.0. (See accompanying
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// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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//
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#ifndef ASIO_QUERY_HPP
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#define ASIO_QUERY_HPP
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#if defined(_MSC_VER) && (_MSC_VER >= 1200)
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# pragma once
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#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
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#include "asio/detail/config.hpp"
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#include "asio/detail/type_traits.hpp"
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#include "asio/is_applicable_property.hpp"
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#include "asio/traits/query_member.hpp"
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#include "asio/traits/query_free.hpp"
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#include "asio/traits/static_query.hpp"
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#include "asio/detail/push_options.hpp"
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#if defined(GENERATING_DOCUMENTATION)
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namespace asio {
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/// A customisation point that queries the value of a property.
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/**
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* The name <tt>query</tt> denotes a customization point object. The
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* expression <tt>asio::query(E, P)</tt> for some
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* subexpressions <tt>E</tt> and <tt>P</tt> (with types <tt>T =
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* decay_t<decltype(E)></tt> and <tt>Prop = decay_t<decltype(P)></tt>) is
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* expression-equivalent to:
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*
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* @li If <tt>is_applicable_property_v<T, Prop></tt> is not a well-formed
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* constant expression with value <tt>true</tt>, <tt>asio::query(E,
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* P)</tt> is ill-formed.
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*
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* @li Otherwise, <tt>Prop::template static_query_v<T></tt> if the expression
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* <tt>Prop::template static_query_v<T></tt> is a well-formed constant
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* expression.
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*
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* @li Otherwise, <tt>(E).query(P)</tt> if the expression
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* <tt>(E).query(P)</tt> is well-formed.
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*
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* @li Otherwise, <tt>query(E, P)</tt> if the expression
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* <tt>query(E, P)</tt> is a valid expression with overload
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* resolution performed in a context that does not include the declaration
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* of the <tt>query</tt> customization point object.
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*
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* @li Otherwise, <tt>asio::query(E, P)</tt> is ill-formed.
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*/
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inline constexpr unspecified query = unspecified;
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/// A type trait that determines whether a @c query expression is well-formed.
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/**
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* Class template @c can_query is a trait that is derived from
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* @c true_type if the expression <tt>asio::query(std::declval<T>(),
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* std::declval<Property>())</tt> is well formed; otherwise @c false_type.
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*/
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template <typename T, typename Property>
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struct can_query :
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integral_constant<bool, automatically_determined>
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{
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};
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/// A type trait that determines whether a @c query expression will
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/// not throw.
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/**
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* Class template @c is_nothrow_query is a trait that is derived from
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* @c true_type if the expression <tt>asio::query(std::declval<T>(),
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* std::declval<Property>())</tt> is @c noexcept; otherwise @c false_type.
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*/
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template <typename T, typename Property>
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struct is_nothrow_query :
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integral_constant<bool, automatically_determined>
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{
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};
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/// A type trait that determines the result type of a @c query expression.
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/**
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* Class template @c query_result is a trait that determines the result
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* type of the expression <tt>asio::query(std::declval<T>(),
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* std::declval<Property>())</tt>.
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*/
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template <typename T, typename Property>
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struct query_result
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{
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/// The result of the @c query expression.
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typedef automatically_determined type;
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};
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} // namespace asio
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#else // defined(GENERATING_DOCUMENTATION)
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namespace asio_query_fn {
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using asio::conditional;
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using asio::decay;
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using asio::declval;
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using asio::enable_if;
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using asio::is_applicable_property;
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using asio::traits::query_free;
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using asio::traits::query_member;
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using asio::traits::static_query;
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void query();
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enum overload_type
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{
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static_value,
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call_member,
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call_free,
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ill_formed
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};
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template <typename Impl, typename T, typename Properties,
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typename = void, typename = void, typename = void, typename = void>
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struct call_traits
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{
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ASIO_STATIC_CONSTEXPR(overload_type, overload = ill_formed);
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ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
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typedef void result_type;
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};
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template <typename Impl, typename T, typename Property>
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struct call_traits<Impl, T, void(Property),
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typename enable_if<
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is_applicable_property<
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typename decay<T>::type,
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typename decay<Property>::type
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>::value
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>::type,
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typename enable_if<
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static_query<T, Property>::is_valid
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>::type> :
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static_query<T, Property>
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{
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ASIO_STATIC_CONSTEXPR(overload_type, overload = static_value);
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};
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template <typename Impl, typename T, typename Property>
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struct call_traits<Impl, T, void(Property),
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typename enable_if<
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is_applicable_property<
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typename decay<T>::type,
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typename decay<Property>::type
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>::value
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>::type,
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typename enable_if<
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!static_query<T, Property>::is_valid
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>::type,
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typename enable_if<
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query_member<typename Impl::template proxy<T>::type, Property>::is_valid
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>::type> :
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query_member<typename Impl::template proxy<T>::type, Property>
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{
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ASIO_STATIC_CONSTEXPR(overload_type, overload = call_member);
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};
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template <typename Impl, typename T, typename Property>
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struct call_traits<Impl, T, void(Property),
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typename enable_if<
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is_applicable_property<
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typename decay<T>::type,
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typename decay<Property>::type
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>::value
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>::type,
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typename enable_if<
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!static_query<T, Property>::is_valid
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>::type,
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typename enable_if<
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!query_member<typename Impl::template proxy<T>::type, Property>::is_valid
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>::type,
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typename enable_if<
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query_free<T, Property>::is_valid
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>::type> :
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query_free<T, Property>
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{
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ASIO_STATIC_CONSTEXPR(overload_type, overload = call_free);
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};
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struct impl
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{
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template <typename T>
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struct proxy
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{
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#if defined(ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
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struct type
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{
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template <typename P>
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auto query(ASIO_MOVE_ARG(P) p)
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noexcept(
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noexcept(
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declval<typename conditional<true, T, P>::type>().query(
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ASIO_MOVE_CAST(P)(p))
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)
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)
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-> decltype(
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declval<typename conditional<true, T, P>::type>().query(
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ASIO_MOVE_CAST(P)(p))
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);
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};
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#else // defined(ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
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typedef T type;
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#endif // defined(ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
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};
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template <typename T, typename Property>
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ASIO_NODISCARD ASIO_CONSTEXPR typename enable_if<
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call_traits<impl, T, void(Property)>::overload == static_value,
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typename call_traits<impl, T, void(Property)>::result_type
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>::type
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operator()(
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ASIO_MOVE_ARG(T),
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ASIO_MOVE_ARG(Property)) const
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ASIO_NOEXCEPT_IF((
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call_traits<impl, T, void(Property)>::is_noexcept))
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{
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return static_query<
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typename decay<T>::type,
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typename decay<Property>::type
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>::value();
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}
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template <typename T, typename Property>
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ASIO_NODISCARD ASIO_CONSTEXPR typename enable_if<
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call_traits<impl, T, void(Property)>::overload == call_member,
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typename call_traits<impl, T, void(Property)>::result_type
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>::type
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operator()(
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ASIO_MOVE_ARG(T) t,
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ASIO_MOVE_ARG(Property) p) const
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ASIO_NOEXCEPT_IF((
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call_traits<impl, T, void(Property)>::is_noexcept))
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{
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return ASIO_MOVE_CAST(T)(t).query(ASIO_MOVE_CAST(Property)(p));
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}
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template <typename T, typename Property>
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ASIO_NODISCARD ASIO_CONSTEXPR typename enable_if<
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call_traits<impl, T, void(Property)>::overload == call_free,
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typename call_traits<impl, T, void(Property)>::result_type
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>::type
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operator()(
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ASIO_MOVE_ARG(T) t,
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ASIO_MOVE_ARG(Property) p) const
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ASIO_NOEXCEPT_IF((
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call_traits<impl, T, void(Property)>::is_noexcept))
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{
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return query(ASIO_MOVE_CAST(T)(t), ASIO_MOVE_CAST(Property)(p));
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}
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};
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template <typename T = impl>
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struct static_instance
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{
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static const T instance;
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};
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template <typename T>
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const T static_instance<T>::instance = {};
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} // namespace asio_query_fn
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namespace asio {
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namespace {
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static ASIO_CONSTEXPR const asio_query_fn::impl&
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query = asio_query_fn::static_instance<>::instance;
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} // namespace
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typedef asio_query_fn::impl query_t;
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template <typename T, typename Property>
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struct can_query :
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integral_constant<bool,
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asio_query_fn::call_traits<query_t, T, void(Property)>::overload !=
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asio_query_fn::ill_formed>
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{
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};
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#if defined(ASIO_HAS_VARIABLE_TEMPLATES)
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template <typename T, typename Property>
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constexpr bool can_query_v
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= can_query<T, Property>::value;
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#endif // defined(ASIO_HAS_VARIABLE_TEMPLATES)
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template <typename T, typename Property>
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struct is_nothrow_query :
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integral_constant<bool,
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asio_query_fn::call_traits<query_t, T, void(Property)>::is_noexcept>
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{
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};
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#if defined(ASIO_HAS_VARIABLE_TEMPLATES)
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template <typename T, typename Property>
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constexpr bool is_nothrow_query_v
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= is_nothrow_query<T, Property>::value;
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#endif // defined(ASIO_HAS_VARIABLE_TEMPLATES)
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template <typename T, typename Property>
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struct query_result
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{
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typedef typename asio_query_fn::call_traits<
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query_t, T, void(Property)>::result_type type;
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};
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} // namespace asio
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#endif // defined(GENERATING_DOCUMENTATION)
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#include "asio/detail/pop_options.hpp"
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#endif // ASIO_QUERY_HPP
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