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- //
- // async_result.hpp
- // ~~~~~~~~~~~~~~~~
- //
- // Copyright (c) 2003-2018 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_ASYNC_RESULT_HPP
- #define BOOST_ASIO_ASYNC_RESULT_HPP
- #if defined(_MSC_VER) && (_MSC_VER >= 1200)
- # pragma once
- #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
- #include <boost/asio/detail/config.hpp>
- #include <boost/asio/detail/type_traits.hpp>
- #include <boost/asio/handler_type.hpp>
- #include <boost/asio/detail/push_options.hpp>
- namespace boost {
- namespace asio {
- /// An interface for customising the behaviour of an initiating function.
- /**
- * The async_result traits class is used for determining:
- *
- * @li the concrete completion handler type to be called at the end of the
- * asynchronous operation;
- *
- * @li the initiating function return type; and
- *
- * @li how the return value of the initiating function is obtained.
- *
- * The trait allows the handler and return types to be determined at the point
- * where the specific completion handler signature is known.
- *
- * This template may be specialised for user-defined completion token types.
- * The primary template assumes that the CompletionToken is the completion
- * handler.
- */
- #if defined(BOOST_ASIO_NO_DEPRECATED) || defined(GENERATING_DOCUMENTATION)
- template <typename CompletionToken, typename Signature>
- #else // defined(BOOST_ASIO_NO_DEPRECATED) || defined(GENERATING_DOCUMENTATION)
- template <typename CompletionToken, typename Signature = void>
- #endif // defined(BOOST_ASIO_NO_DEPRECATED) || defined(GENERATING_DOCUMENTATION)
- class async_result
- {
- public:
- #if defined(BOOST_ASIO_NO_DEPRECATED) || defined(GENERATING_DOCUMENTATION)
- /// The concrete completion handler type for the specific signature.
- typedef CompletionToken completion_handler_type;
- /// The return type of the initiating function.
- typedef void return_type;
- #else // defined(BOOST_ASIO_NO_DEPRECATED) || defined(GENERATING_DOCUMENTATION)
- // For backward compatibility, determine the concrete completion handler type
- // by using the legacy handler_type trait.
- typedef typename handler_type<CompletionToken, Signature>::type
- completion_handler_type;
- // For backward compatibility, determine the initiating function return type
- // using the legacy single-parameter version of async_result.
- typedef typename async_result<completion_handler_type>::type return_type;
- #endif // defined(BOOST_ASIO_NO_DEPRECATED) || defined(GENERATING_DOCUMENTATION)
- /// Construct an async result from a given handler.
- /**
- * When using a specalised async_result, the constructor has an opportunity
- * to initialise some state associated with the completion handler, which is
- * then returned from the initiating function.
- */
- explicit async_result(completion_handler_type& h)
- #if defined(BOOST_ASIO_NO_DEPRECATED) || defined(GENERATING_DOCUMENTATION)
- // No data members to initialise.
- #else // defined(BOOST_ASIO_NO_DEPRECATED) || defined(GENERATING_DOCUMENTATION)
- : legacy_result_(h)
- #endif // defined(BOOST_ASIO_NO_DEPRECATED) || defined(GENERATING_DOCUMENTATION)
- {
- (void)h;
- }
- /// Obtain the value to be returned from the initiating function.
- return_type get()
- {
- #if defined(BOOST_ASIO_NO_DEPRECATED) || defined(GENERATING_DOCUMENTATION)
- // Nothing to do.
- #else // defined(BOOST_ASIO_NO_DEPRECATED) || defined(GENERATING_DOCUMENTATION)
- return legacy_result_.get();
- #endif // defined(BOOST_ASIO_NO_DEPRECATED) || defined(GENERATING_DOCUMENTATION)
- }
- private:
- async_result(const async_result&) BOOST_ASIO_DELETED;
- async_result& operator=(const async_result&) BOOST_ASIO_DELETED;
- #if defined(BOOST_ASIO_NO_DEPRECATED) || defined(GENERATING_DOCUMENTATION)
- // No data members.
- #else // defined(BOOST_ASIO_NO_DEPRECATED) || defined(GENERATING_DOCUMENTATION)
- async_result<completion_handler_type> legacy_result_;
- #endif // defined(BOOST_ASIO_NO_DEPRECATED) || defined(GENERATING_DOCUMENTATION)
- };
- #if !defined(BOOST_ASIO_NO_DEPRECATED)
- /// (Deprecated: Use two-parameter version of async_result.) An interface for
- /// customising the behaviour of an initiating function.
- /**
- * This template may be specialised for user-defined handler types.
- */
- template <typename Handler>
- class async_result<Handler>
- {
- public:
- /// The return type of the initiating function.
- typedef void type;
- /// Construct an async result from a given handler.
- /**
- * When using a specalised async_result, the constructor has an opportunity
- * to initialise some state associated with the handler, which is then
- * returned from the initiating function.
- */
- explicit async_result(Handler&)
- {
- }
- /// Obtain the value to be returned from the initiating function.
- type get()
- {
- }
- };
- #endif // !defined(BOOST_ASIO_NO_DEPRECATED)
- /// Helper template to deduce the handler type from a CompletionToken, capture
- /// a local copy of the handler, and then create an async_result for the
- /// handler.
- template <typename CompletionToken, typename Signature>
- struct async_completion
- {
- /// The real handler type to be used for the asynchronous operation.
- typedef typename boost::asio::async_result<
- typename decay<CompletionToken>::type,
- Signature>::completion_handler_type completion_handler_type;
- #if defined(BOOST_ASIO_HAS_MOVE) || defined(GENERATING_DOCUMENTATION)
- /// Constructor.
- /**
- * The constructor creates the concrete completion handler and makes the link
- * between the handler and the asynchronous result.
- */
- explicit async_completion(CompletionToken& token)
- : completion_handler(static_cast<typename conditional<
- is_same<CompletionToken, completion_handler_type>::value,
- completion_handler_type&, CompletionToken&&>::type>(token)),
- result(completion_handler)
- {
- }
- #else // defined(BOOST_ASIO_HAS_MOVE) || defined(GENERATING_DOCUMENTATION)
- explicit async_completion(typename decay<CompletionToken>::type& token)
- : completion_handler(token),
- result(completion_handler)
- {
- }
- explicit async_completion(const typename decay<CompletionToken>::type& token)
- : completion_handler(token),
- result(completion_handler)
- {
- }
- #endif // defined(BOOST_ASIO_HAS_MOVE) || defined(GENERATING_DOCUMENTATION)
- /// A copy of, or reference to, a real handler object.
- #if defined(BOOST_ASIO_HAS_MOVE) || defined(GENERATING_DOCUMENTATION)
- typename conditional<
- is_same<CompletionToken, completion_handler_type>::value,
- completion_handler_type&, completion_handler_type>::type completion_handler;
- #else // defined(BOOST_ASIO_HAS_MOVE) || defined(GENERATING_DOCUMENTATION)
- completion_handler_type completion_handler;
- #endif // defined(BOOST_ASIO_HAS_MOVE) || defined(GENERATING_DOCUMENTATION)
- /// The result of the asynchronous operation's initiating function.
- async_result<typename decay<CompletionToken>::type, Signature> result;
- };
- namespace detail {
- template <typename CompletionToken, typename Signature>
- struct async_result_helper
- : async_result<typename decay<CompletionToken>::type, Signature>
- {
- };
- } // namespace detail
- } // namespace asio
- } // namespace boost
- #include <boost/asio/detail/pop_options.hpp>
- #if defined(GENERATING_DOCUMENTATION)
- # define BOOST_ASIO_INITFN_RESULT_TYPE(ct, sig) \
- void_or_deduced
- #elif defined(_MSC_VER) && (_MSC_VER < 1500)
- # define BOOST_ASIO_INITFN_RESULT_TYPE(ct, sig) \
- typename ::boost::asio::detail::async_result_helper< \
- ct, sig>::return_type
- #define BOOST_ASIO_HANDLER_TYPE(ct, sig) \
- typename ::boost::asio::detail::async_result_helper< \
- ct, sig>::completion_handler_type
- #else
- # define BOOST_ASIO_INITFN_RESULT_TYPE(ct, sig) \
- typename ::boost::asio::async_result< \
- typename ::boost::asio::decay<ct>::type, sig>::return_type
- #define BOOST_ASIO_HANDLER_TYPE(ct, sig) \
- typename ::boost::asio::async_result< \
- typename ::boost::asio::decay<ct>::type, sig>::completion_handler_type
- #endif
- #endif // BOOST_ASIO_ASYNC_RESULT_HPP
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