1 //
2 // traits/equality_comparable.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_EQUALITY_COMPARABLE_HPP
12 #define BOOST_ASIO_TRAITS_EQUALITY_COMPARABLE_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_EQUALITY_COMPARABLE_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 namespace boost {
30 namespace asio {
31 namespace traits {
32 
33 template <typename T, typename = void>
34 struct equality_comparable_default;
35 
36 template <typename T, typename = void>
37 struct equality_comparable;
38 
39 } // namespace traits
40 namespace detail {
41 
42 struct no_equality_comparable
43 {
44   BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = false);
45   BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
46 };
47 
48 #if defined(BOOST_ASIO_HAS_DEDUCED_EQUALITY_COMPARABLE_TRAIT)
49 
50 template <typename T, typename = void>
51 struct equality_comparable_trait : no_equality_comparable
52 {
53 };
54 
55 template <typename T>
56 struct equality_comparable_trait<T,
57   typename void_type<
58     decltype(
59       static_cast<void>(
60         static_cast<bool>(declval<const T>() == declval<const T>())
61       ),
62       static_cast<void>(
63         static_cast<bool>(declval<const T>() != declval<const T>())
64       )
65     )
66   >::type>
67 {
68   BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
69 
70   BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept =
71     noexcept(declval<const T>() == declval<const T>())
72       && noexcept(declval<const T>() != declval<const T>()));
73 };
74 
75 #else // defined(BOOST_ASIO_HAS_DEDUCED_EQUALITY_COMPARABLE_TRAIT)
76 
77 template <typename T, typename = void>
78 struct equality_comparable_trait :
79   conditional<
80     is_same<T, typename decay<T>::type>::value,
81     no_equality_comparable,
82     traits::equality_comparable<typename decay<T>::type>
83   >::type
84 {
85 };
86 
87 #endif // defined(BOOST_ASIO_HAS_DEDUCED_EQUALITY_COMPARABLE_TRAIT)
88 
89 } // namespace detail
90 namespace traits {
91 
92 template <typename T, typename>
93 struct equality_comparable_default : detail::equality_comparable_trait<T>
94 {
95 };
96 
97 template <typename T, typename>
98 struct equality_comparable : equality_comparable_default<T>
99 {
100 };
101 
102 } // namespace traits
103 } // namespace asio
104 } // namespace boost
105 
106 #endif // BOOST_ASIO_TRAITS_EQUALITY_COMPARABLE_HPP
107