| // |
| // uses_executor.hpp |
| // ~~~~~~~~~~~~~~~~~ |
| // |
| // Copyright (c) 2003-2015 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 |