332 lines
9.0 KiB
C++
332 lines
9.0 KiB
C++
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//
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// execution/prefer_only.hpp
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// ~~~~~~~~~~~~~~~~~~~~~~~~~
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//
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// Copyright (c) 2003-2023 Christopher M. Kohlhoff (chris at kohlhoff dot com)
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//
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// Distributed under the Boost Software License, Version 1.0. (See accompanying
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// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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//
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#ifndef ASIO_EXECUTION_PREFER_ONLY_HPP
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#define ASIO_EXECUTION_PREFER_ONLY_HPP
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#if defined(_MSC_VER) && (_MSC_VER >= 1200)
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# pragma once
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#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
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#include "asio/detail/config.hpp"
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#include "asio/detail/type_traits.hpp"
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#include "asio/is_applicable_property.hpp"
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#include "asio/prefer.hpp"
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#include "asio/query.hpp"
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#include "asio/traits/static_query.hpp"
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#include "asio/detail/push_options.hpp"
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namespace asio {
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#if defined(GENERATING_DOCUMENTATION)
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namespace execution {
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/// A property adapter that is used with the polymorphic executor wrapper
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/// to mark properties as preferable, but not requirable.
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template <typename Property>
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struct prefer_only
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{
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/// The prefer_only adapter applies to the same types as the nested property.
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template <typename T>
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static constexpr bool is_applicable_property_v =
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is_applicable_property<T, Property>::value;
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/// The context_t property cannot be required.
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static constexpr bool is_requirable = false;
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/// The context_t property can be preferred, it the underlying property can
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/// be preferred.
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/**
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* @c true if @c Property::is_preferable is @c true, otherwise @c false.
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*/
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static constexpr bool is_preferable = automatically_determined;
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/// The type returned by queries against an @c any_executor.
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typedef typename Property::polymorphic_query_result_type
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polymorphic_query_result_type;
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};
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} // namespace execution
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#else // defined(GENERATING_DOCUMENTATION)
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namespace execution {
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namespace detail {
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template <typename InnerProperty, typename = void>
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struct prefer_only_is_preferable
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{
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ASIO_STATIC_CONSTEXPR(bool, is_preferable = false);
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};
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template <typename InnerProperty>
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struct prefer_only_is_preferable<InnerProperty,
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typename enable_if<
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InnerProperty::is_preferable
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>::type>
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{
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ASIO_STATIC_CONSTEXPR(bool, is_preferable = true);
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};
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template <typename InnerProperty, typename = void>
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struct prefer_only_polymorphic_query_result_type
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{
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};
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template <typename InnerProperty>
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struct prefer_only_polymorphic_query_result_type<InnerProperty,
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typename void_type<
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typename InnerProperty::polymorphic_query_result_type
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>::type>
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{
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typedef typename InnerProperty::polymorphic_query_result_type
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polymorphic_query_result_type;
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};
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template <typename InnerProperty, typename = void>
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struct prefer_only_property
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{
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InnerProperty property;
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prefer_only_property(const InnerProperty& p)
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: property(p)
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{
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}
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};
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#if defined(ASIO_HAS_DECLTYPE) \
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&& defined(ASIO_HAS_WORKING_EXPRESSION_SFINAE)
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template <typename InnerProperty>
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struct prefer_only_property<InnerProperty,
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typename void_type<
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decltype(asio::declval<const InnerProperty>().value())
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>::type>
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{
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InnerProperty property;
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prefer_only_property(const InnerProperty& p)
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: property(p)
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{
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}
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ASIO_CONSTEXPR auto value() const
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ASIO_NOEXCEPT_IF((
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noexcept(asio::declval<const InnerProperty>().value())))
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-> decltype(asio::declval<const InnerProperty>().value())
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{
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return property.value();
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}
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};
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#else // defined(ASIO_HAS_DECLTYPE)
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// && defined(ASIO_HAS_WORKING_EXPRESSION_SFINAE)
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struct prefer_only_memfns_base
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{
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void value();
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};
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template <typename T>
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struct prefer_only_memfns_derived
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: T, prefer_only_memfns_base
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{
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};
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template <typename T, T>
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struct prefer_only_memfns_check
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{
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};
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template <typename>
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char (&prefer_only_value_memfn_helper(...))[2];
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template <typename T>
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char prefer_only_value_memfn_helper(
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prefer_only_memfns_check<
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void (prefer_only_memfns_base::*)(),
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&prefer_only_memfns_derived<T>::value>*);
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template <typename InnerProperty>
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struct prefer_only_property<InnerProperty,
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typename enable_if<
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sizeof(prefer_only_value_memfn_helper<InnerProperty>(0)) != 1
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&& !is_same<typename InnerProperty::polymorphic_query_result_type,
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void>::value
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>::type>
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{
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InnerProperty property;
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prefer_only_property(const InnerProperty& p)
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: property(p)
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{
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}
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ASIO_CONSTEXPR typename InnerProperty::polymorphic_query_result_type
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value() const
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{
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return property.value();
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}
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};
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#endif // defined(ASIO_HAS_DECLTYPE)
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// && defined(ASIO_HAS_WORKING_EXPRESSION_SFINAE)
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} // namespace detail
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template <typename InnerProperty>
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struct prefer_only :
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detail::prefer_only_is_preferable<InnerProperty>,
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detail::prefer_only_polymorphic_query_result_type<InnerProperty>,
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detail::prefer_only_property<InnerProperty>
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{
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ASIO_STATIC_CONSTEXPR(bool, is_requirable = false);
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ASIO_CONSTEXPR prefer_only(const InnerProperty& p)
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: detail::prefer_only_property<InnerProperty>(p)
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{
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}
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#if defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
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&& defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
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template <typename T>
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static ASIO_CONSTEXPR
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typename traits::static_query<T, InnerProperty>::result_type
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static_query()
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ASIO_NOEXCEPT_IF((
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traits::static_query<T, InnerProperty>::is_noexcept))
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{
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return traits::static_query<T, InnerProperty>::value();
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}
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template <typename E, typename T = decltype(prefer_only::static_query<E>())>
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static ASIO_CONSTEXPR const T static_query_v
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= prefer_only::static_query<E>();
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#endif // defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
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// && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
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template <typename Executor, typename Property>
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friend ASIO_CONSTEXPR
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typename prefer_result<const Executor&, const InnerProperty&>::type
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prefer(const Executor& ex, const prefer_only<Property>& p,
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typename enable_if<
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is_same<Property, InnerProperty>::value
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>::type* = 0,
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typename enable_if<
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can_prefer<const Executor&, const InnerProperty&>::value
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>::type* = 0)
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#if !defined(ASIO_MSVC) \
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&& !defined(__clang__) // Clang crashes if noexcept is used here.
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ASIO_NOEXCEPT_IF((
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is_nothrow_prefer<const Executor&, const InnerProperty&>::value))
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#endif // !defined(ASIO_MSVC)
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// && !defined(__clang__)
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{
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return asio::prefer(ex, p.property);
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}
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template <typename Executor, typename Property>
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friend ASIO_CONSTEXPR
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typename query_result<const Executor&, const InnerProperty&>::type
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query(const Executor& ex, const prefer_only<Property>& p,
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typename enable_if<
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is_same<Property, InnerProperty>::value
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>::type* = 0,
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typename enable_if<
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can_query<const Executor&, const InnerProperty&>::value
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>::type* = 0)
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#if !defined(ASIO_MSVC) \
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&& !defined(__clang__) // Clang crashes if noexcept is used here.
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ASIO_NOEXCEPT_IF((
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is_nothrow_query<const Executor&, const InnerProperty&>::value))
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#endif // !defined(ASIO_MSVC)
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// && !defined(__clang__)
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{
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return asio::query(ex, p.property);
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}
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};
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#if defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
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&& defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
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template <typename InnerProperty> template <typename E, typename T>
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const T prefer_only<InnerProperty>::static_query_v;
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#endif // defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
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// && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
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} // namespace execution
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template <typename T, typename InnerProperty>
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struct is_applicable_property<T, execution::prefer_only<InnerProperty> >
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: is_applicable_property<T, InnerProperty>
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{
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};
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namespace traits {
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#if !defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
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|| !defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
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template <typename T, typename InnerProperty>
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struct static_query<T, execution::prefer_only<InnerProperty> > :
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static_query<T, const InnerProperty&>
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{
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};
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#endif // !defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
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// || !defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
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#if !defined(ASIO_HAS_DEDUCED_PREFER_FREE_TRAIT)
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template <typename T, typename InnerProperty>
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struct prefer_free_default<T, execution::prefer_only<InnerProperty>,
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typename enable_if<
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can_prefer<const T&, const InnerProperty&>::value
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>::type>
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{
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ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
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ASIO_STATIC_CONSTEXPR(bool, is_noexcept =
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(is_nothrow_prefer<const T&, const InnerProperty&>::value));
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typedef typename prefer_result<const T&,
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const InnerProperty&>::type result_type;
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};
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#endif // !defined(ASIO_HAS_DEDUCED_PREFER_FREE_TRAIT)
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#if !defined(ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
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template <typename T, typename InnerProperty>
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struct query_free<T, execution::prefer_only<InnerProperty>,
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typename enable_if<
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can_query<const T&, const InnerProperty&>::value
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>::type>
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{
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ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
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ASIO_STATIC_CONSTEXPR(bool, is_noexcept =
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(is_nothrow_query<const T&, const InnerProperty&>::value));
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typedef typename query_result<const T&,
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const InnerProperty&>::type result_type;
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};
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#endif // !defined(ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)
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} // namespace traits
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#endif // defined(GENERATING_DOCUMENTATION)
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} // namespace asio
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#include "asio/detail/pop_options.hpp"
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#endif // ASIO_EXECUTION_PREFER_ONLY_HPP
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