| // |
| // execution/context_as.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_EXECUTION_CONTEXT_AS_HPP |
| #define ASIO_EXECUTION_CONTEXT_AS_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/execution/executor.hpp" |
| #include "asio/execution/scheduler.hpp" |
| #include "asio/execution/sender.hpp" |
| #include "asio/is_applicable_property.hpp" |
| #include "asio/query.hpp" |
| #include "asio/traits/query_static_constexpr_member.hpp" |
| #include "asio/traits/static_query.hpp" |
| |
| #include "asio/detail/push_options.hpp" |
| |
| namespace asio { |
| |
| #if defined(GENERATING_DOCUMENTATION) |
| |
| namespace execution { |
| |
| /// A property that is used to obtain the execution context that is associated |
| /// with an executor. |
| template <typename U> |
| struct context_as_t |
| { |
| /// The context_as_t property applies to executors, senders, and schedulers. |
| template <typename T> |
| static constexpr bool is_applicable_property_v = |
| is_executor_v<T> || is_sender_v<T> || is_scheduler_v<T>; |
| |
| /// The context_t property cannot be required. |
| static constexpr bool is_requirable = false; |
| |
| /// The context_t property cannot be preferred. |
| static constexpr bool is_preferable = false; |
| |
| /// The type returned by queries against an @c any_executor. |
| typedef T polymorphic_query_result_type; |
| }; |
| |
| /// A special value used for accessing the context_as_t property. |
| template <typename U> |
| constexpr context_as_t context_as; |
| |
| } // namespace execution |
| |
| #else // defined(GENERATING_DOCUMENTATION) |
| |
| namespace execution { |
| |
| template <typename T> |
| struct context_as_t |
| { |
| #if defined(ASIO_HAS_VARIABLE_TEMPLATES) |
| template <typename U> |
| ASIO_STATIC_CONSTEXPR(bool, |
| is_applicable_property_v = ( |
| is_executor<U>::value |
| || conditional< |
| is_executor<U>::value, |
| false_type, |
| is_sender<U> |
| >::type::value |
| || conditional< |
| is_executor<U>::value, |
| false_type, |
| is_scheduler<U> |
| >::type::value)); |
| #endif // defined(ASIO_HAS_VARIABLE_TEMPLATES) |
| |
| ASIO_STATIC_CONSTEXPR(bool, is_requirable = false); |
| ASIO_STATIC_CONSTEXPR(bool, is_preferable = false); |
| |
| typedef T polymorphic_query_result_type; |
| |
| ASIO_CONSTEXPR context_as_t() |
| { |
| } |
| |
| ASIO_CONSTEXPR context_as_t(context_t) |
| { |
| } |
| |
| #if defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \ |
| && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES) |
| template <typename E> |
| static ASIO_CONSTEXPR |
| typename traits::query_static_constexpr_member<E, context_t>::result_type |
| static_query() |
| ASIO_NOEXCEPT_IF(( |
| traits::query_static_constexpr_member<E, context_t>::is_noexcept)) |
| { |
| return traits::query_static_constexpr_member<E, context_t>::value(); |
| } |
| |
| template <typename E, typename U = decltype(context_as_t::static_query<E>())> |
| static ASIO_CONSTEXPR const U static_query_v |
| = context_as_t::static_query<E>(); |
| #endif // defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) |
| // && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES) |
| |
| template <typename Executor, typename U> |
| friend ASIO_CONSTEXPR U query( |
| const Executor& ex, const context_as_t<U>&, |
| typename enable_if< |
| is_same<T, U>::value |
| >::type* = 0, |
| typename enable_if< |
| can_query<const Executor&, const context_t&>::value |
| >::type* = 0) |
| #if !defined(__clang__) // Clang crashes if noexcept is used here. |
| #if defined(ASIO_MSVC) // Visual C++ wants the type to be qualified. |
| ASIO_NOEXCEPT_IF(( |
| is_nothrow_query<const Executor&, const context_t&>::value)) |
| #else // defined(ASIO_MSVC) |
| ASIO_NOEXCEPT_IF(( |
| is_nothrow_query<const Executor&, const context_t&>::value)) |
| #endif // defined(ASIO_MSVC) |
| #endif // !defined(__clang__) |
| { |
| return asio::query(ex, context); |
| } |
| }; |
| |
| #if defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \ |
| && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES) |
| template <typename T> template <typename E, typename U> |
| const U context_as_t<T>::static_query_v; |
| #endif // defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) |
| // && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES) |
| |
| #if (defined(ASIO_HAS_VARIABLE_TEMPLATES) \ |
| && defined(ASIO_HAS_CONSTEXPR)) \ |
| || defined(GENERATING_DOCUMENTATION) |
| template <typename T> |
| constexpr context_as_t<T> context_as{}; |
| #endif // (defined(ASIO_HAS_VARIABLE_TEMPLATES) |
| // && defined(ASIO_HAS_CONSTEXPR)) |
| // || defined(GENERATING_DOCUMENTATION) |
| |
| } // namespace execution |
| |
| #if !defined(ASIO_HAS_VARIABLE_TEMPLATES) |
| |
| template <typename T, typename U> |
| struct is_applicable_property<T, execution::context_as_t<U> > |
| : integral_constant<bool, |
| execution::is_executor<T>::value |
| || conditional< |
| execution::is_executor<T>::value, |
| false_type, |
| execution::is_sender<T> |
| >::type::value |
| || conditional< |
| execution::is_executor<T>::value, |
| false_type, |
| execution::is_scheduler<T> |
| >::type::value> |
| { |
| }; |
| |
| #endif // !defined(ASIO_HAS_VARIABLE_TEMPLATES) |
| |
| namespace traits { |
| |
| #if !defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \ |
| || !defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES) |
| |
| template <typename T, typename U> |
| struct static_query<T, execution::context_as_t<U>, |
| typename enable_if< |
| static_query<T, execution::context_t>::is_valid |
| >::type> : static_query<T, execution::context_t> |
| { |
| }; |
| |
| #endif // !defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) |
| // || !defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES) |
| |
| #if !defined(ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT) |
| |
| template <typename T, typename U> |
| struct query_free<T, execution::context_as_t<U>, |
| typename enable_if< |
| can_query<const T&, const execution::context_t&>::value |
| >::type> |
| { |
| ASIO_STATIC_CONSTEXPR(bool, is_valid = true); |
| ASIO_STATIC_CONSTEXPR(bool, is_noexcept = |
| (is_nothrow_query<const T&, const execution::context_t&>::value)); |
| |
| typedef U result_type; |
| }; |
| |
| #endif // !defined(ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT) |
| |
| } // namespace traits |
| |
| #endif // defined(GENERATING_DOCUMENTATION) |
| |
| } // namespace asio |
| |
| #include "asio/detail/pop_options.hpp" |
| |
| #endif // ASIO_EXECUTION_CONTEXT_AS_HPP |