Warning: This file is not a C or C++ file. It does not have highlighting.

1//===----------------------------------------------------------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8
9#ifndef _LIBCPP___TYPE_TRAITS_COMMON_TYPE_H
10#define _LIBCPP___TYPE_TRAITS_COMMON_TYPE_H
11
12#include <__config>
13#include <__type_traits/conditional.h>
14#include <__type_traits/decay.h>
15#include <__type_traits/is_same.h>
16#include <__type_traits/remove_cvref.h>
17#include <__type_traits/type_identity.h>
18#include <__type_traits/void_t.h>
19#include <__utility/declval.h>
20#include <__utility/empty.h>
21
22#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
23# pragma GCC system_header
24#endif
25
26_LIBCPP_BEGIN_NAMESPACE_STD
27
28#if __has_builtin(__builtin_common_type)
29
30template <class... _Args>
31struct common_type;
32
33template <class... _Args>
34using __common_type_t _LIBCPP_NODEBUG = typename common_type<_Args...>::type;
35
36template <class... _Args>
37struct common_type : __builtin_common_type<__common_type_t, __type_identity, __empty, _Args...> {};
38
39#else
40# if _LIBCPP_STD_VER >= 20
41// Let COND_RES(X, Y) be:
42template <class _Tp, class _Up>
43using __cond_type _LIBCPP_NODEBUG = decltype(false ? std::declval<_Tp>() : std::declval<_Up>());
44
45template <class _Tp, class _Up, class = void>
46struct __common_type3 {};
47
48// sub-bullet 4 - "if COND_RES(CREF(D1), CREF(D2)) denotes a type..."
49template <class _Tp, class _Up>
50struct __common_type3<_Tp, _Up, void_t<__cond_type<const _Tp&, const _Up&>>> {
51 using type _LIBCPP_NODEBUG = remove_cvref_t<__cond_type<const _Tp&, const _Up&>>;
52};
53
54template <class _Tp, class _Up, class = void>
55struct __common_type2_imp : __common_type3<_Tp, _Up> {};
56# else
57template <class _Tp, class _Up, class = void>
58struct __common_type2_imp {};
59# endif
60
61// sub-bullet 3 - "if decay_t<decltype(false ? declval<D1>() : declval<D2>())> ..."
62template <class _Tp, class _Up>
63struct __common_type2_imp<_Tp, _Up, __void_t<decltype(true ? std::declval<_Tp>() : std::declval<_Up>())> > {
64 using type _LIBCPP_NODEBUG = __decay_t<decltype(true ? std::declval<_Tp>() : std::declval<_Up>())>;
65};
66
67template <class, class = void>
68struct __common_type_impl {};
69
70template <class... _Tp>
71struct __common_types;
72template <class... _Tp>
73struct common_type;
74
75template <class _Tp, class _Up>
76struct __common_type_impl< __common_types<_Tp, _Up>, __void_t<typename common_type<_Tp, _Up>::type> > {
77 typedef typename common_type<_Tp, _Up>::type type;
78};
79
80template <class _Tp, class _Up, class _Vp, class... _Rest>
81struct __common_type_impl<__common_types<_Tp, _Up, _Vp, _Rest...>, __void_t<typename common_type<_Tp, _Up>::type> >
82 : __common_type_impl<__common_types<typename common_type<_Tp, _Up>::type, _Vp, _Rest...> > {};
83
84// bullet 1 - sizeof...(Tp) == 0
85
86template <>
87struct common_type<> {};
88
89// bullet 2 - sizeof...(Tp) == 1
90
91template <class _Tp>
92struct common_type<_Tp> : public common_type<_Tp, _Tp> {};
93
94// bullet 3 - sizeof...(Tp) == 2
95
96// sub-bullet 1 - "If is_same_v<T1, D1> is false or ..."
97template <class _Tp, class _Up>
98struct common_type<_Tp, _Up>
99 : __conditional_t<_IsSame<_Tp, __decay_t<_Tp> >::value && _IsSame<_Up, __decay_t<_Up> >::value,
100 __common_type2_imp<_Tp, _Up>,
101 common_type<__decay_t<_Tp>, __decay_t<_Up> > > {};
102
103// bullet 4 - sizeof...(Tp) > 2
104
105template <class _Tp, class _Up, class _Vp, class... _Rest>
106struct common_type<_Tp, _Up, _Vp, _Rest...> : __common_type_impl<__common_types<_Tp, _Up, _Vp, _Rest...> > {};
107
108#endif
109
110#if _LIBCPP_STD_VER >= 14
111template <class... _Tp>
112using common_type_t = typename common_type<_Tp...>::type;
113#endif
114
115_LIBCPP_END_NAMESPACE_STD
116
117#endif // _LIBCPP___TYPE_TRAITS_COMMON_TYPE_H
118

Warning: This file is not a C or C++ file. It does not have highlighting.

source code of libcxx/include/__type_traits/common_type.h