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 ASIO_ASYNC_RESULT_HPP
12#define ASIO_ASYNC_RESULT_HPP
13
14
15#include "asio/detail/config.hpp"
16#include "asio/handler_type.hpp"
17
18#include "asio/detail/push_options.hpp"
19
20namespace asio {
21
22/// An interface for customising the behaviour of an initiating function.
23/**
24 * This template may be specialised for user-defined handler types.
25 */
26template <typename Handler>
27class async_result
28{
29public:
30  /// The return type of the initiating function.
31  typedef void type;
32
33  /// Construct an async result from a given handler.
34  /**
35   * When using a specalised async_result, the constructor has an opportunity
36   * to initialise some state associated with the handler, which is then
37   * returned from the initiating function.
38   */
39  explicit async_result(Handler&)
40  {
41  }
42
43  /// Obtain the value to be returned from the initiating function.
44  type get()
45  {
46  }
47};
48
49namespace detail {
50
51// Helper template to deduce the true type of a handler, capture a local copy
52// of the handler, and then create an async_result for the handler.
53template <typename Handler, typename Signature>
54struct async_result_init
55{
56  explicit async_result_init(ASIO_MOVE_ARG(Handler) orig_handler)
57    : handler(ASIO_MOVE_CAST(Handler)(orig_handler)),
58      result(handler)
59  {
60  }
61
62  typename handler_type<Handler, Signature>::type handler;
63  async_result<typename handler_type<Handler, Signature>::type> result;
64};
65
66template <typename Handler, typename Signature>
67struct async_result_type_helper
68{
69  typedef typename async_result<
70      typename handler_type<Handler, Signature>::type
71    >::type type;
72};
73
74} // namespace detail
75} // namespace asio
76
77#include "asio/detail/pop_options.hpp"
78
79# define ASIO_INITFN_RESULT_TYPE(h, sig)    typename ::asio::async_result<      typename ::asio::handler_type<h, sig>::type>::type
80
81#endif // ASIO_ASYNC_RESULT_HPP
82