1 //
2 // traits/start_member.hpp
3 // ~~~~~~~~~~~~~~~~~~~~~~~
4 //
5 // Copyright (c) 2003-2021 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_TRAITS_START_MEMBER_HPP
12 #define BOOST_ASIO_TRAITS_START_MEMBER_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/detail/type_traits.hpp>
20 
21 #if defined(BOOST_ASIO_HAS_DECLTYPE) \
22   && defined(BOOST_ASIO_HAS_NOEXCEPT) \
23   && defined(BOOST_ASIO_HAS_WORKING_EXPRESSION_SFINAE)
24 # define BOOST_ASIO_HAS_DEDUCED_START_MEMBER_TRAIT 1
25 #endif // defined(BOOST_ASIO_HAS_DECLTYPE)
26        //   && defined(BOOST_ASIO_HAS_NOEXCEPT)
27        //   && defined(BOOST_ASIO_HAS_WORKING_EXPRESSION_SFINAE)
28 
29 #include <boost/asio/detail/push_options.hpp>
30 
31 namespace boost {
32 namespace asio {
33 namespace traits {
34 
35 template <typename T, typename = void>
36 struct start_member_default;
37 
38 template <typename T, typename = void>
39 struct start_member;
40 
41 } // namespace traits
42 namespace detail {
43 
44 struct no_start_member
45 {
46   BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = false);
47   BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
48 };
49 
50 #if defined(BOOST_ASIO_HAS_DEDUCED_START_MEMBER_TRAIT)
51 
52 template <typename T, typename = void>
53 struct start_member_trait : no_start_member
54 {
55 };
56 
57 template <typename T>
58 struct start_member_trait<T,
59   typename void_type<
60     decltype(declval<T>().start())
61   >::type>
62 {
63   BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
64 
65   using result_type = decltype(declval<T>().start());
66 
67   BOOST_ASIO_STATIC_CONSTEXPR(bool,
68     is_noexcept = noexcept(declval<T>().start()));
69 };
70 
71 #else // defined(BOOST_ASIO_HAS_DEDUCED_START_MEMBER_TRAIT)
72 
73 template <typename T, typename = void>
74 struct start_member_trait :
75   conditional<
76     is_same<T, typename remove_reference<T>::type>::value,
77     typename conditional<
78       is_same<T, typename add_const<T>::type>::value,
79       no_start_member,
80       traits::start_member<typename add_const<T>::type>
81     >::type,
82     traits::start_member<typename remove_reference<T>::type>
83   >::type
84 {
85 };
86 
87 #endif // defined(BOOST_ASIO_HAS_DEDUCED_START_MEMBER_TRAIT)
88 
89 } // namespace detail
90 namespace traits {
91 
92 template <typename T, typename>
93 struct start_member_default :
94   detail::start_member_trait<T>
95 {
96 };
97 
98 template <typename T, typename>
99 struct start_member :
100   start_member_default<T>
101 {
102 };
103 
104 } // namespace traits
105 } // namespace asio
106 } // namespace boost
107 
108 #include <boost/asio/detail/pop_options.hpp>
109 
110 #endif // BOOST_ASIO_TRAITS_START_MEMBER_HPP
111