137 lines
4.4 KiB
C++
137 lines
4.4 KiB
C++
//
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// experimental/as_single.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_EXPERIMENTAL_AS_SINGLE_HPP
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#define ASIO_EXPERIMENTAL_AS_SINGLE_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/detail/push_options.hpp"
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namespace asio {
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namespace experimental {
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/// A @ref completion_token adapter used to specify that the completion handler
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/// arguments should be combined into a single argument.
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/**
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* The as_single_t class is used to indicate that any arguments to the
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* completion handler should be combined and passed as a single argument.
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* If there is already one argument, that argument is passed as-is. If
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* there is more than argument, the arguments are first moved into a
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* @c std::tuple and that tuple is then passed to the completion handler.
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*/
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template <typename CompletionToken>
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class as_single_t
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{
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public:
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/// Tag type used to prevent the "default" constructor from being used for
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/// conversions.
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struct default_constructor_tag {};
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/// Default constructor.
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/**
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* This constructor is only valid if the underlying completion token is
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* default constructible and move constructible. The underlying completion
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* token is itself defaulted as an argument to allow it to capture a source
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* location.
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*/
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ASIO_CONSTEXPR as_single_t(
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default_constructor_tag = default_constructor_tag(),
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CompletionToken token = CompletionToken())
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: token_(ASIO_MOVE_CAST(CompletionToken)(token))
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{
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}
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/// Constructor.
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template <typename T>
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ASIO_CONSTEXPR explicit as_single_t(
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ASIO_MOVE_ARG(T) completion_token)
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: token_(ASIO_MOVE_CAST(T)(completion_token))
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{
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}
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/// Adapts an executor to add the @c as_single_t completion token as the
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/// default.
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template <typename InnerExecutor>
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struct executor_with_default : InnerExecutor
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{
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/// Specify @c as_single_t as the default completion token type.
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typedef as_single_t default_completion_token_type;
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/// Construct the adapted executor from the inner executor type.
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executor_with_default(const InnerExecutor& ex) ASIO_NOEXCEPT
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: InnerExecutor(ex)
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{
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}
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/// Convert the specified executor to the inner executor type, then use
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/// that to construct the adapted executor.
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template <typename OtherExecutor>
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executor_with_default(const OtherExecutor& ex,
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typename constraint<
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is_convertible<OtherExecutor, InnerExecutor>::value
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>::type = 0) ASIO_NOEXCEPT
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: InnerExecutor(ex)
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{
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}
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};
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/// Type alias to adapt an I/O object to use @c as_single_t as its
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/// default completion token type.
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#if defined(ASIO_HAS_ALIAS_TEMPLATES) \
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|| defined(GENERATING_DOCUMENTATION)
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template <typename T>
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using as_default_on_t = typename T::template rebind_executor<
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executor_with_default<typename T::executor_type> >::other;
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#endif // defined(ASIO_HAS_ALIAS_TEMPLATES)
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// || defined(GENERATING_DOCUMENTATION)
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/// Function helper to adapt an I/O object to use @c as_single_t as its
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/// default completion token type.
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template <typename T>
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static typename decay<T>::type::template rebind_executor<
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executor_with_default<typename decay<T>::type::executor_type>
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>::other
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as_default_on(ASIO_MOVE_ARG(T) object)
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{
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return typename decay<T>::type::template rebind_executor<
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executor_with_default<typename decay<T>::type::executor_type>
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>::other(ASIO_MOVE_CAST(T)(object));
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}
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//private:
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CompletionToken token_;
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};
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/// Adapt a @ref completion_token to specify that the completion handler
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/// arguments should be combined into a single argument.
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template <typename CompletionToken>
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ASIO_NODISCARD inline
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ASIO_CONSTEXPR as_single_t<typename decay<CompletionToken>::type>
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as_single(ASIO_MOVE_ARG(CompletionToken) completion_token)
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{
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return as_single_t<typename decay<CompletionToken>::type>(
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ASIO_MOVE_CAST(CompletionToken)(completion_token));
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}
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} // namespace experimental
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} // namespace asio
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#include "asio/detail/pop_options.hpp"
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#include "asio/experimental/impl/as_single.hpp"
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#endif // ASIO_EXPERIMENTAL_AS_SINGLE_HPP
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