| // |
| // associated_executor.hpp |
| // ~~~~~~~~~~~~~~~~~~~~~~~ |
| // |
| // Copyright (c) 2003-2020 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_ASSOCIATED_EXECUTOR_HPP |
| #define ASIO_ASSOCIATED_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_context.hpp" |
| #include "asio/is_executor.hpp" |
| |
| #include "asio/detail/push_options.hpp" |
| |
| namespace asio { |
| namespace detail { |
| |
| template <typename> |
| struct associated_executor_check |
| { |
| typedef void type; |
| }; |
| |
| template <typename T, typename E, typename = void> |
| struct associated_executor_impl |
| { |
| typedef E type; |
| |
| static type get(const T&, const E& e) ASIO_NOEXCEPT |
| { |
| return e; |
| } |
| }; |
| |
| template <typename T, typename E> |
| struct associated_executor_impl<T, E, |
| typename associated_executor_check<typename T::executor_type>::type> |
| { |
| typedef typename T::executor_type type; |
| |
| static type get(const T& t, const E&) ASIO_NOEXCEPT |
| { |
| return t.get_executor(); |
| } |
| }; |
| |
| } // namespace detail |
| |
| /// Traits type used to obtain the executor associated with an object. |
| /** |
| * A program may specialise this traits type if the @c T template parameter in |
| * the specialisation is a user-defined type. The template parameter @c |
| * Executor shall be a type meeting the Executor requirements. |
| * |
| * Specialisations shall meet the following requirements, where @c t is a const |
| * reference to an object of type @c T, and @c e is an object of type @c |
| * Executor. |
| * |
| * @li Provide a nested typedef @c type that identifies a type meeting the |
| * Executor requirements. |
| * |
| * @li Provide a noexcept static member function named @c get, callable as @c |
| * get(t) and with return type @c type. |
| * |
| * @li Provide a noexcept static member function named @c get, callable as @c |
| * get(t,e) and with return type @c type. |
| */ |
| template <typename T, typename Executor> |
| struct associated_executor |
| { |
| /// If @c T has a nested type @c executor_type, <tt>T::executor_type</tt>. |
| /// Otherwise @c Executor. |
| #if defined(GENERATING_DOCUMENTATION) |
| typedef see_below type; |
| #else // defined(GENERATING_DOCUMENTATION) |
| typedef typename detail::associated_executor_impl<T, Executor>::type type; |
| #endif // defined(GENERATING_DOCUMENTATION) |
| |
| /// If @c T has a nested type @c executor_type, returns |
| /// <tt>t.get_executor()</tt>. Otherwise returns @c ex. |
| static type get(const T& t, const Executor& ex) ASIO_NOEXCEPT |
| { |
| return detail::associated_executor_impl<T, Executor>::get(t, ex); |
| } |
| }; |
| |
| /// Helper function to obtain an object's associated executor. |
| /** |
| * @returns <tt>associated_executor<T, Executor>::get(t, ex)</tt> |
| */ |
| template <typename T, typename Executor> |
| inline typename associated_executor<T, Executor>::type |
| get_associated_executor(const T& t, const Executor& ex, |
| typename enable_if<is_executor< |
| Executor>::value>::type* = 0) ASIO_NOEXCEPT |
| { |
| return associated_executor<T, Executor>::get(t, ex); |
| } |
| |
| /// Helper function to obtain an object's associated executor. |
| /** |
| * @returns <tt>associated_executor<T, typename |
| * ExecutionContext::executor_type>::get(t, ctx.get_executor())</tt> |
| */ |
| template <typename T, typename ExecutionContext> |
| inline typename associated_executor<T, |
| typename ExecutionContext::executor_type>::type |
| get_associated_executor(const T& t, ExecutionContext& ctx, |
| typename enable_if<is_convertible<ExecutionContext&, |
| execution_context&>::value>::type* = 0) ASIO_NOEXCEPT |
| { |
| return associated_executor<T, |
| typename ExecutionContext::executor_type>::get(t, ctx.get_executor()); |
| } |
| |
| #if defined(ASIO_HAS_ALIAS_TEMPLATES) |
| |
| template <typename T, typename Executor> |
| using associated_executor_t = typename associated_executor<T, Executor>::type; |
| |
| #endif // defined(ASIO_HAS_ALIAS_TEMPLATES) |
| |
| } // namespace asio |
| |
| #include "asio/detail/pop_options.hpp" |
| |
| #endif // ASIO_ASSOCIATED_EXECUTOR_HPP |