1 // 2 // async_result.hpp 3 // ~~~~~~~~~~~~~~~~ 4 // 5 // Copyright (c) 2003-2015 Christopher M. Kohlhoff (chris at kohlhoff dot com) 6 // 7 // Distributed under the Boost Software License, Version 1.0. (See accompanying 8 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) 9 // 10 11 #ifndef BOOST_ASIO_ASYNC_RESULT_HPP 12 #define BOOST_ASIO_ASYNC_RESULT_HPP 13 14 #if defined(_MSC_VER) && (_MSC_VER >= 1200) 15 # pragma once 16 #endif // defined(_MSC_VER) && (_MSC_VER >= 1200) 17 18 #include <boost/asio/detail/config.hpp> 19 #include <boost/asio/handler_type.hpp> 20 21 #include <boost/asio/detail/push_options.hpp> 22 23 namespace boost { 24 namespace asio { 25 26 /// An interface for customising the behaviour of an initiating function. 27 /** 28 * This template may be specialised for user-defined handler types. 29 */ 30 template <typename Handler> 31 class async_result 32 { 33 public: 34 /// The return type of the initiating function. 35 typedef void type; 36 37 /// Construct an async result from a given handler. 38 /** 39 * When using a specalised async_result, the constructor has an opportunity 40 * to initialise some state associated with the handler, which is then 41 * returned from the initiating function. 42 */ async_result(Handler &)43 explicit async_result(Handler&) 44 { 45 } 46 47 /// Obtain the value to be returned from the initiating function. get()48 type get() 49 { 50 } 51 }; 52 53 namespace detail { 54 55 // Helper template to deduce the true type of a handler, capture a local copy 56 // of the handler, and then create an async_result for the handler. 57 template <typename Handler, typename Signature> 58 struct async_result_init 59 { async_result_initboost::asio::detail::async_result_init60 explicit async_result_init(BOOST_ASIO_MOVE_ARG(Handler) orig_handler) 61 : handler(BOOST_ASIO_MOVE_CAST(Handler)(orig_handler)), 62 result(handler) 63 { 64 } 65 66 typename handler_type<Handler, Signature>::type handler; 67 async_result<typename handler_type<Handler, Signature>::type> result; 68 }; 69 70 template <typename Handler, typename Signature> 71 struct async_result_type_helper 72 { 73 typedef typename async_result< 74 typename handler_type<Handler, Signature>::type 75 >::type type; 76 }; 77 78 } // namespace detail 79 } // namespace asio 80 } // namespace boost 81 82 #include <boost/asio/detail/pop_options.hpp> 83 84 #if defined(GENERATING_DOCUMENTATION) 85 # define BOOST_ASIO_INITFN_RESULT_TYPE(h, sig) \ 86 void_or_deduced 87 #elif defined(_MSC_VER) && (_MSC_VER < 1500) 88 # define BOOST_ASIO_INITFN_RESULT_TYPE(h, sig) \ 89 typename ::boost::asio::detail::async_result_type_helper<h, sig>::type 90 #else 91 # define BOOST_ASIO_INITFN_RESULT_TYPE(h, sig) \ 92 typename ::boost::asio::async_result< \ 93 typename ::boost::asio::handler_type<h, sig>::type>::type 94 #endif 95 96 #endif // BOOST_ASIO_ASYNC_RESULT_HPP 97