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- //
- // use_awaitable.hpp
- // ~~~~~~~~~~~~~~~~~
- //
- // Copyright (c) 2003-2019 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 BOOST_ASIO_USE_AWAITABLE_HPP
- #define BOOST_ASIO_USE_AWAITABLE_HPP
- #if defined(_MSC_VER) && (_MSC_VER >= 1200)
- # pragma once
- #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
- #include <boost/asio/detail/config.hpp>
- #if defined(BOOST_ASIO_HAS_CO_AWAIT) || defined(GENERATING_DOCUMENTATION)
- #include <boost/asio/awaitable.hpp>
- #include <boost/asio/detail/push_options.hpp>
- namespace boost {
- namespace asio {
- /// A completion token that represents the currently executing coroutine.
- /**
- * The @c use_awaitable_t class, with its value @c use_awaitable, is used to
- * represent the currently executing coroutine. This completion token may be
- * passed as a handler to an asynchronous operation. For example:
- *
- * @code awaitable<void> my_coroutine()
- * {
- * std::size_t n = co_await my_socket.async_read_some(buffer, use_awaitable);
- * ...
- * } @endcode
- *
- * When used with co_await, the initiating function (@c async_read_some in the
- * above example) suspends the current coroutine. The coroutine is resumed when
- * the asynchronous operation completes, and the result of the operation is
- * returned.
- */
- template <typename Executor = executor>
- struct use_awaitable_t
- {
- /// Default constructor.
- BOOST_ASIO_CONSTEXPR use_awaitable_t()
- {
- }
- /// Adapts an executor to add the @c use_awaitable_t completion token as the
- /// default.
- template <typename InnerExecutor>
- struct executor_with_default : InnerExecutor
- {
- /// Specify @c use_awaitable_t as the default completion token type.
- typedef use_awaitable_t default_completion_token_type;
- /// Construct the adapted executor from the inner executor type.
- executor_with_default(const InnerExecutor& ex) BOOST_ASIO_NOEXCEPT
- : InnerExecutor(ex)
- {
- }
- };
- /// Type alias to adapt an I/O object to use @c use_awaitable_t as its
- /// default completion token type.
- #if defined(BOOST_ASIO_HAS_ALIAS_TEMPLATES) \
- || defined(GENERATING_DOCUMENTATION)
- template <typename T>
- using as_default_on_t = typename T::template rebind_executor<
- executor_with_default<typename T::executor_type> >::other;
- #endif // defined(BOOST_ASIO_HAS_ALIAS_TEMPLATES)
- // || defined(GENERATING_DOCUMENTATION)
- /// Function helper to adapt an I/O object to use @c use_awaitable_t as its
- /// default completion token type.
- template <typename T>
- static typename T::template rebind_executor<
- executor_with_default<typename T::executor_type>
- >::other
- as_default_on(BOOST_ASIO_MOVE_ARG(T) object)
- {
- return typename as_default_on_t<typename decay<T>::type>::type(
- BOOST_ASIO_MOVE_CAST(T)(object));
- }
- };
- /// A completion token object that represents the currently executing coroutine.
- /**
- * See the documentation for boost::asio::use_awaitable_t for a usage example.
- */
- #if defined(BOOST_ASIO_HAS_CONSTEXPR) || defined(GENERATING_DOCUMENTATION)
- constexpr use_awaitable_t<> use_awaitable;
- #elif defined(BOOST_ASIO_MSVC)
- __declspec(selectany) use_awaitable_t<> use_awaitable;
- #endif
- } // namespace asio
- } // namespace boost
- #include <boost/asio/detail/pop_options.hpp>
- #include <boost/asio/impl/use_awaitable.hpp>
- #endif // defined(BOOST_ASIO_HAS_CO_AWAIT) || defined(GENERATING_DOCUMENTATION)
- #endif // BOOST_ASIO_USE_AWAITABLE_HPP
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