1#ifndef BOOST_TYPE_TRAITS_COMMON_TYPE_HPP_INCLUDED
2#define BOOST_TYPE_TRAITS_COMMON_TYPE_HPP_INCLUDED
3
4//
5// Copyright 2015 Peter Dimov
6//
7// Distributed under the Boost Software License, Version 1.0.
8// See accompanying file LICENSE_1_0.txt or copy at
9// http://www.boost.org/LICENSE_1_0.txt
10//
11
12#include <boost/config.hpp>
13#include <boost/type_traits/decay.hpp>
14#include <boost/type_traits/declval.hpp>
15#include <boost/detail/workaround.hpp>
16
17#if defined(BOOST_NO_CXX11_DECLTYPE)
18#include <boost/type_traits/detail/common_type_impl.hpp>
19#endif
20
21#if !defined(BOOST_NO_CXX11_TEMPLATE_ALIASES) && !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES)
22#include <boost/type_traits/detail/mp_defer.hpp>
23#endif
24
25namespace boost
26{
27
28// variadic common_type
29
30#if !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES)
31
32template<class... T> struct common_type
33{
34};
35
36#if !defined(BOOST_NO_CXX11_TEMPLATE_ALIASES)
37
38template<class... T> using common_type_t = typename common_type<T...>::type;
39
40namespace type_traits_detail
41{
42
43template<class T1, class T2, class... T> using common_type_fold = common_type_t<common_type_t<T1, T2>, T...>;
44
45} // namespace type_traits_detail
46
47template<class T1, class T2, class... T>
48struct common_type<T1, T2, T...>: type_traits_detail::mp_defer<type_traits_detail::common_type_fold, T1, T2, T...>
49{
50};
51
52#else
53
54template<class T1, class T2, class... T>
55struct common_type<T1, T2, T...>: common_type<typename common_type<T1, T2>::type, T...>
56{
57};
58
59#endif // !defined(BOOST_NO_CXX11_TEMPLATE_ALIASES)
60
61#else
62
63template<
64 class T1 = void, class T2 = void, class T3 = void,
65 class T4 = void, class T5 = void, class T6 = void,
66 class T7 = void, class T8 = void, class T9 = void
67>
68struct common_type: common_type<typename common_type<T1, T2>::type, T3, T4, T5, T6, T7, T8, T9>
69{
70};
71
72#endif // !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES)
73
74// one argument
75
76template<class T> struct common_type<T>: boost::decay<T>
77{
78};
79
80// two arguments
81
82namespace type_traits_detail
83{
84
85// binary common_type
86
87#if !defined(BOOST_NO_CXX11_DECLTYPE)
88
89#if !defined(BOOST_NO_CXX11_TEMPLATE_ALIASES) && !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES)
90
91#if !defined(BOOST_MSVC) || BOOST_MSVC > 1800
92
93// internal compiler error on msvc-12.0
94
95template<class T1, class T2> using builtin_common_type = typename boost::decay<decltype( boost::declval<bool>()? boost::declval<T1>(): boost::declval<T2>() )>::type;
96
97template<class T1, class T2> struct common_type_impl: mp_defer<builtin_common_type, T1, T2>
98{
99};
100
101#else
102
103template<class T1, class T2> using builtin_common_type = decltype( boost::declval<bool>()? boost::declval<T1>(): boost::declval<T2>() );
104
105template<class T1, class T2> struct common_type_impl_2: mp_defer<builtin_common_type, T1, T2>
106{
107};
108
109template<class T1, class T2> using decay_common_type = typename boost::decay<typename common_type_impl_2<T1, T2>::type>::type;
110
111template<class T1, class T2> struct common_type_impl: mp_defer<decay_common_type, T1, T2>
112{
113};
114
115#endif // !defined(BOOST_MSVC) || BOOST_MSVC > 1800
116
117#else
118
119template<class T1, class T2> struct common_type_impl: boost::decay<decltype( boost::declval<bool>()? boost::declval<T1>(): boost::declval<T2>() )>
120{
121};
122
123#endif // #if !defined(BOOST_NO_CXX11_TEMPLATE_ALIASES) && !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES)
124
125#endif // #if !defined(BOOST_NO_CXX11_DECLTYPE)
126
127// decay helper
128
129template<class T1, class T2, class T1d = typename boost::decay<T1>::type, class T2d = typename boost::decay<T2>::type> struct common_type_decay_helper: boost::common_type<T1d, T2d>
130{
131};
132
133template<class T1, class T2> struct common_type_decay_helper<T1, T2, T1, T2>: common_type_impl<T1, T2>
134{
135};
136
137} // type_traits_detail
138
139template<class T1, class T2> struct common_type<T1, T2>: type_traits_detail::common_type_decay_helper<T1, T2>
140{
141};
142
143} // namespace boost
144
145#endif // #ifndef BOOST_TYPE_TRAITS_COMMON_TYPE_HPP_INCLUDED
146