| // |
| // execution/prefer_only.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_PREFER_ONLY_HPP |
| #define ASIO_EXECUTION_PREFER_ONLY_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/is_applicable_property.hpp" |
| #include "asio/prefer.hpp" |
| #include "asio/query.hpp" |
| #include "asio/traits/static_query.hpp" |
| |
| #include "asio/detail/push_options.hpp" |
| |
| namespace asio { |
| |
| #if defined(GENERATING_DOCUMENTATION) |
| |
| namespace execution { |
| |
| /// A property adapter that is used with the polymorphic executor wrapper |
| /// to mark properties as preferable, but not requirable. |
| template <typename Property> |
| struct prefer_only |
| { |
| /// The prefer_only adapter applies to the same types as the nested property. |
| template <typename T> |
| static constexpr bool is_applicable_property_v = |
| is_applicable_property<T, Property>::value; |
| |
| /// The context_t property cannot be required. |
| static constexpr bool is_requirable = false; |
| |
| /// The context_t property can be preferred, it the underlying property can |
| /// be preferred. |
| /** |
| * @c true if @c Property::is_preferable is @c true, otherwise @c false. |
| */ |
| static constexpr bool is_preferable = automatically_determined; |
| |
| /// The type returned by queries against an @c any_executor. |
| typedef typename Property::polymorphic_query_result_type |
| polymorphic_query_result_type; |
| }; |
| |
| } // namespace execution |
| |
| #else // defined(GENERATING_DOCUMENTATION) |
| |
| namespace execution { |
| namespace detail { |
| |
| template <typename InnerProperty, typename = void> |
| struct prefer_only_is_preferable |
| { |
| ASIO_STATIC_CONSTEXPR(bool, is_preferable = false); |
| }; |
| |
| template <typename InnerProperty> |
| struct prefer_only_is_preferable<InnerProperty, |
| typename enable_if< |
| InnerProperty::is_preferable |
| >::type> |
| { |
| ASIO_STATIC_CONSTEXPR(bool, is_preferable = true); |
| }; |
| |
| template <typename InnerProperty, typename = void> |
| struct prefer_only_polymorphic_query_result_type |
| { |
| }; |
| |
| template <typename InnerProperty> |
| struct prefer_only_polymorphic_query_result_type<InnerProperty, |
| typename void_type< |
| typename InnerProperty::polymorphic_query_result_type |
| >::type> |
| { |
| typedef typename InnerProperty::polymorphic_query_result_type |
| polymorphic_query_result_type; |
| }; |
| |
| template <typename InnerProperty, typename = void, typename = void> |
| struct prefer_only_property |
| { |
| InnerProperty property; |
| |
| prefer_only_property(const InnerProperty& p) |
| : property(p) |
| { |
| } |
| }; |
| |
| #if defined(ASIO_HAS_DECLTYPE) \ |
| && defined(ASIO_HAS_WORKING_EXPRESSION_SFINAE) |
| |
| template <typename InnerProperty> |
| struct prefer_only_property<InnerProperty, |
| typename void_type< |
| decltype(asio::declval<const InnerProperty>().value()) |
| >::type> |
| { |
| InnerProperty property; |
| |
| prefer_only_property(const InnerProperty& p) |
| : property(p) |
| { |
| } |
| |
| ASIO_CONSTEXPR auto value() const |
| ASIO_NOEXCEPT_IF(( |
| noexcept(asio::declval<const InnerProperty>().value()))) |
| -> decltype(asio::declval<const InnerProperty>().value()) |
| { |
| return property.value(); |
| } |
| }; |
| |
| #else // defined(ASIO_HAS_DECLTYPE) |
| // && defined(ASIO_HAS_WORKING_EXPRESSION_SFINAE) |
| |
| struct prefer_only_memfns_base |
| { |
| void value(); |
| }; |
| |
| template <typename T> |
| struct prefer_only_memfns_derived |
| : T, prefer_only_memfns_base |
| { |
| }; |
| |
| template <typename T, T> |
| struct prefer_only_memfns_check |
| { |
| }; |
| |
| template <typename> |
| char (&prefer_only_value_memfn_helper(...))[2]; |
| |
| template <typename T> |
| char prefer_only_value_memfn_helper( |
| prefer_only_memfns_check< |
| void (prefer_only_memfns_base::*)(), |
| &prefer_only_memfns_derived<T>::value>*); |
| |
| template <typename InnerProperty> |
| struct prefer_only_property<InnerProperty, |
| typename enable_if< |
| sizeof(prefer_only_value_memfn_helper<InnerProperty>(0)) != 1 |
| >::type, |
| typename enable_if< |
| !is_same< |
| typename InnerProperty::polymorphic_query_result_type, |
| void |
| >::value |
| >::type> |
| { |
| InnerProperty property; |
| |
| prefer_only_property(const InnerProperty& p) |
| : property(p) |
| { |
| } |
| |
| ASIO_CONSTEXPR typename InnerProperty::polymorphic_query_result_type |
| value() const |
| { |
| return property.value(); |
| } |
| }; |
| |
| #endif // defined(ASIO_HAS_DECLTYPE) |
| // && defined(ASIO_HAS_WORKING_EXPRESSION_SFINAE) |
| |
| } // namespace detail |
| |
| template <typename InnerProperty> |
| struct prefer_only : |
| detail::prefer_only_is_preferable<InnerProperty>, |
| detail::prefer_only_polymorphic_query_result_type<InnerProperty>, |
| detail::prefer_only_property<InnerProperty> |
| { |
| ASIO_STATIC_CONSTEXPR(bool, is_requirable = false); |
| |
| ASIO_CONSTEXPR prefer_only(const InnerProperty& p) |
| : detail::prefer_only_property<InnerProperty>(p) |
| { |
| } |
| |
| #if defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \ |
| && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES) |
| template <typename T> |
| static ASIO_CONSTEXPR |
| typename traits::static_query<T, InnerProperty>::result_type |
| static_query() |
| ASIO_NOEXCEPT_IF(( |
| traits::static_query<T, InnerProperty>::is_noexcept)) |
| { |
| return traits::static_query<T, InnerProperty>::value(); |
| } |
| |
| template <typename E, typename T = decltype(prefer_only::static_query<E>())> |
| static ASIO_CONSTEXPR const T static_query_v |
| = prefer_only::static_query<E>(); |
| #endif // defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) |
| // && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES) |
| |
| template <typename Executor, typename Property> |
| friend ASIO_CONSTEXPR |
| typename prefer_result<const Executor&, const InnerProperty&>::type |
| prefer(const Executor& ex, const prefer_only<Property>& p, |
| typename enable_if< |
| is_same<Property, InnerProperty>::value |
| >::type* = 0, |
| typename enable_if< |
| can_prefer<const Executor&, const InnerProperty&>::value |
| >::type* = 0) |
| #if !defined(ASIO_MSVC) \ |
| && !defined(__clang__) // Clang crashes if noexcept is used here. |
| ASIO_NOEXCEPT_IF(( |
| is_nothrow_prefer<const Executor&, const InnerProperty&>::value)) |
| #endif // !defined(ASIO_MSVC) |
| // && !defined(__clang__) |
| { |
| return asio::prefer(ex, p.property); |
| } |
| |
| template <typename Executor, typename Property> |
| friend ASIO_CONSTEXPR |
| typename query_result<const Executor&, const InnerProperty&>::type |
| query(const Executor& ex, const prefer_only<Property>& p, |
| typename enable_if< |
| is_same<Property, InnerProperty>::value |
| >::type* = 0, |
| typename enable_if< |
| can_query<const Executor&, const InnerProperty&>::value |
| >::type* = 0) |
| #if !defined(ASIO_MSVC) \ |
| && !defined(__clang__) // Clang crashes if noexcept is used here. |
| ASIO_NOEXCEPT_IF(( |
| is_nothrow_query<const Executor&, const InnerProperty&>::value)) |
| #endif // !defined(ASIO_MSVC) |
| // && !defined(__clang__) |
| { |
| return asio::query(ex, p.property); |
| } |
| }; |
| |
| #if defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \ |
| && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES) |
| template <typename InnerProperty> template <typename E, typename T> |
| const T prefer_only<InnerProperty>::static_query_v; |
| #endif // defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) |
| // && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES) |
| |
| } // namespace execution |
| |
| template <typename T, typename InnerProperty> |
| struct is_applicable_property<T, execution::prefer_only<InnerProperty> > |
| : is_applicable_property<T, InnerProperty> |
| { |
| }; |
| |
| namespace traits { |
| |
| #if !defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \ |
| || !defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES) |
| |
| template <typename T, typename InnerProperty> |
| struct static_query<T, execution::prefer_only<InnerProperty> > : |
| static_query<T, const InnerProperty&> |
| { |
| }; |
| |
| #endif // !defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) |
| // || !defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES) |
| |
| #if !defined(ASIO_HAS_DEDUCED_PREFER_FREE_TRAIT) |
| |
| template <typename T, typename InnerProperty> |
| struct prefer_free_default<T, execution::prefer_only<InnerProperty>, |
| typename enable_if< |
| can_prefer<const T&, const InnerProperty&>::value |
| >::type> |
| { |
| ASIO_STATIC_CONSTEXPR(bool, is_valid = true); |
| ASIO_STATIC_CONSTEXPR(bool, is_noexcept = |
| (is_nothrow_prefer<const T&, const InnerProperty&>::value)); |
| |
| typedef typename prefer_result<const T&, |
| const InnerProperty&>::type result_type; |
| }; |
| |
| #endif // !defined(ASIO_HAS_DEDUCED_PREFER_FREE_TRAIT) |
| |
| #if !defined(ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT) |
| |
| template <typename T, typename InnerProperty> |
| struct query_free<T, execution::prefer_only<InnerProperty>, |
| typename enable_if< |
| can_query<const T&, const InnerProperty&>::value |
| >::type> |
| { |
| ASIO_STATIC_CONSTEXPR(bool, is_valid = true); |
| ASIO_STATIC_CONSTEXPR(bool, is_noexcept = |
| (is_nothrow_query<const T&, const InnerProperty&>::value)); |
| |
| typedef typename query_result<const T&, |
| const InnerProperty&>::type 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_PREFER_ONLY_HPP |