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/void_t.h> 18#include <__utility/declval.h> 19 20#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) 21# pragma GCC system_header 22#endif 23 24_LIBCPP_BEGIN_NAMESPACE_STD 25 26#if _LIBCPP_STD_VER > 17 27// Let COND_RES(X, Y) be: 28template <class _Tp, class _Up> 29using __cond_type = decltype(false ? std::declval<_Tp>() : std::declval<_Up>()); 30 31template <class _Tp, class _Up, class = void> 32struct __common_type3 {}; 33 34// sub-bullet 4 - "if COND_RES(CREF(D1), CREF(D2)) denotes a type..." 35template <class _Tp, class _Up> 36struct __common_type3<_Tp, _Up, void_t<__cond_type<const _Tp&, const _Up&>>> 37{ 38 using type = remove_cvref_t<__cond_type<const _Tp&, const _Up&>>; 39}; 40 41template <class _Tp, class _Up, class = void> 42struct __common_type2_imp : __common_type3<_Tp, _Up> {}; 43#else 44template <class _Tp, class _Up, class = void> 45struct __common_type2_imp {}; 46#endif 47 48// sub-bullet 3 - "if decay_t<decltype(false ? declval<D1>() : declval<D2>())> ..." 49template <class _Tp, class _Up> 50struct __common_type2_imp<_Tp, _Up, __void_t<decltype(true ? std::declval<_Tp>() : std::declval<_Up>())> > 51{ 52 typedef _LIBCPP_NODEBUG typename decay<decltype( 53 true ? std::declval<_Tp>() : std::declval<_Up>() 54 )>::type type; 55}; 56 57template <class, class = void> 58struct __common_type_impl {}; 59 60// Clang provides variadic templates in C++03 as an extension. 61#if !defined(_LIBCPP_CXX03_LANG) || defined(__clang__) 62# define _LIBCPP_OPTIONAL_PACK(...) , __VA_ARGS__ 63template <class... _Tp> 64struct __common_types; 65template <class... _Tp> 66struct _LIBCPP_TEMPLATE_VIS common_type; 67#else 68# define _LIBCPP_OPTIONAL_PACK(...) 69struct __no_arg; 70template <class _Tp, class _Up, class = __no_arg> 71struct __common_types; 72template <class _Tp = __no_arg, class _Up = __no_arg, class _Vp = __no_arg, 73 class _Unused = __no_arg> 74struct common_type { 75 static_assert(sizeof(_Unused) == 0, 76 "common_type accepts at most 3 arguments in C++03"); 77}; 78#endif // _LIBCPP_CXX03_LANG 79 80template <class _Tp, class _Up> 81struct __common_type_impl< 82 __common_types<_Tp, _Up>, __void_t<typename common_type<_Tp, _Up>::type> > 83{ 84 typedef typename common_type<_Tp, _Up>::type type; 85}; 86 87template <class _Tp, class _Up, class _Vp _LIBCPP_OPTIONAL_PACK(class... _Rest)> 88struct __common_type_impl< 89 __common_types<_Tp, _Up, _Vp _LIBCPP_OPTIONAL_PACK(_Rest...)>, 90 __void_t<typename common_type<_Tp, _Up>::type> > 91 : __common_type_impl<__common_types<typename common_type<_Tp, _Up>::type, 92 _Vp _LIBCPP_OPTIONAL_PACK(_Rest...)> > { 93}; 94 95// bullet 1 - sizeof...(Tp) == 0 96 97template <> 98struct _LIBCPP_TEMPLATE_VIS common_type<> {}; 99 100// bullet 2 - sizeof...(Tp) == 1 101 102template <class _Tp> 103struct _LIBCPP_TEMPLATE_VIS common_type<_Tp> 104 : public common_type<_Tp, _Tp> {}; 105 106// bullet 3 - sizeof...(Tp) == 2 107 108// sub-bullet 1 - "If is_same_v<T1, D1> is false or ..." 109template <class _Tp, class _Up> 110struct _LIBCPP_TEMPLATE_VIS common_type<_Tp, _Up> 111 : conditional< 112 _IsSame<_Tp, typename decay<_Tp>::type>::value && _IsSame<_Up, typename decay<_Up>::type>::value, 113 __common_type2_imp<_Tp, _Up>, 114 common_type<typename decay<_Tp>::type, typename decay<_Up>::type> 115 >::type 116{}; 117 118// bullet 4 - sizeof...(Tp) > 2 119 120template <class _Tp, class _Up, class _Vp _LIBCPP_OPTIONAL_PACK(class... _Rest)> 121struct _LIBCPP_TEMPLATE_VIS 122 common_type<_Tp, _Up, _Vp _LIBCPP_OPTIONAL_PACK(_Rest...)> 123 : __common_type_impl< 124 __common_types<_Tp, _Up, _Vp _LIBCPP_OPTIONAL_PACK(_Rest...)> > {}; 125 126#undef _LIBCPP_OPTIONAL_PACK 127 128#if _LIBCPP_STD_VER > 11 129template <class ..._Tp> using common_type_t = typename common_type<_Tp...>::type; 130#endif 131 132_LIBCPP_END_NAMESPACE_STD 133 134#endif // _LIBCPP___TYPE_TRAITS_COMMON_TYPE_H 135