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- //
- // uses_executor.hpp
- // ~~~~~~~~~~~~~~~~~
- //
- // Copyright (c) 2003-2019 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_USES_EXECUTOR_HPP
- #define ASIO_USES_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/detail/push_options.hpp"
-
- namespace asio {
-
- /// A special type, similar to std::nothrow_t, used to disambiguate
- /// constructors that accept executor arguments.
- /**
- * The executor_arg_t struct is an empty structure type used as a unique type
- * to disambiguate constructor and function overloading. Specifically, some
- * types have constructors with executor_arg_t as the first argument,
- * immediately followed by an argument of a type that satisfies the Executor
- * type requirements.
- */
- struct executor_arg_t
- {
- /// Constructor.
- ASIO_CONSTEXPR executor_arg_t() ASIO_NOEXCEPT
- {
- }
- };
-
- /// A special value, similar to std::nothrow, used to disambiguate constructors
- /// that accept executor arguments.
- /**
- * See asio::executor_arg_t and asio::uses_executor
- * for more information.
- */
- #if defined(ASIO_HAS_CONSTEXPR) || defined(GENERATING_DOCUMENTATION)
- constexpr executor_arg_t executor_arg;
- #elif defined(ASIO_MSVC)
- __declspec(selectany) executor_arg_t executor_arg;
- #endif
-
- /// The uses_executor trait detects whether a type T has an associated executor
- /// that is convertible from type Executor.
- /**
- * Meets the BinaryTypeTrait requirements. The Asio library provides a
- * definition that is derived from false_type. A program may specialize this
- * template to derive from true_type for a user-defined type T that can be
- * constructed with an executor, where the first argument of a constructor has
- * type executor_arg_t and the second argument is convertible from type
- * Executor.
- */
- template <typename T, typename Executor>
- struct uses_executor : false_type {};
-
- } // namespace asio
-
- #include "asio/detail/pop_options.hpp"
-
- #endif // ASIO_USES_EXECUTOR_HPP
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