72 lines
2.2 KiB
C++
72 lines
2.2 KiB
C++
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//
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// uses_executor.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_USES_EXECUTOR_HPP
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#define ASIO_USES_EXECUTOR_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/detail/push_options.hpp"
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namespace asio {
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/// A special type, similar to std::nothrow_t, used to disambiguate
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/// constructors that accept executor arguments.
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/**
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* The executor_arg_t struct is an empty structure type used as a unique type
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* to disambiguate constructor and function overloading. Specifically, some
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* types have constructors with executor_arg_t as the first argument,
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* immediately followed by an argument of a type that satisfies the Executor
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* type requirements.
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*/
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struct executor_arg_t
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{
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/// Constructor.
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ASIO_CONSTEXPR executor_arg_t() ASIO_NOEXCEPT
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{
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}
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};
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/// A special value, similar to std::nothrow, used to disambiguate constructors
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/// that accept executor arguments.
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/**
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* See asio::executor_arg_t and asio::uses_executor
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* for more information.
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*/
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#if defined(ASIO_HAS_CONSTEXPR) || defined(GENERATING_DOCUMENTATION)
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constexpr executor_arg_t executor_arg;
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#elif defined(ASIO_MSVC)
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__declspec(selectany) executor_arg_t executor_arg;
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#endif
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/// The uses_executor trait detects whether a type T has an associated executor
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/// that is convertible from type Executor.
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/**
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* Meets the BinaryTypeTrait requirements. The Asio library provides a
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* definition that is derived from false_type. A program may specialize this
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* template to derive from true_type for a user-defined type T that can be
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* constructed with an executor, where the first argument of a constructor has
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* type executor_arg_t and the second argument is convertible from type
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* Executor.
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*/
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template <typename T, typename Executor>
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struct uses_executor : false_type {};
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} // namespace asio
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#include "asio/detail/pop_options.hpp"
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#endif // ASIO_USES_EXECUTOR_HPP
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