| //===----------------------------------------------------------------------===// |
| // |
| // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| // See https://llvm.org/LICENSE.txt for license information. |
| // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #ifndef _LIBCPP___TYPE_TRAITS_COMMON_TYPE_H |
| #define _LIBCPP___TYPE_TRAITS_COMMON_TYPE_H |
| |
| #include <__config> |
| #include <__type_traits/conditional.h> |
| #include <__type_traits/decay.h> |
| #include <__type_traits/is_same.h> |
| #include <__type_traits/remove_cvref.h> |
| #include <__type_traits/void_t.h> |
| #include <__utility/declval.h> |
| |
| #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) |
| # pragma GCC system_header |
| #endif |
| |
| _LIBCPP_BEGIN_NAMESPACE_STD |
| |
| #if _LIBCPP_STD_VER >= 20 |
| // Let COND_RES(X, Y) be: |
| template <class _Tp, class _Up> |
| using __cond_type = decltype(false ? std::declval<_Tp>() : std::declval<_Up>()); |
| |
| template <class _Tp, class _Up, class = void> |
| struct __common_type3 {}; |
| |
| // sub-bullet 4 - "if COND_RES(CREF(D1), CREF(D2)) denotes a type..." |
| template <class _Tp, class _Up> |
| struct __common_type3<_Tp, _Up, void_t<__cond_type<const _Tp&, const _Up&>>> { |
| using type = remove_cvref_t<__cond_type<const _Tp&, const _Up&>>; |
| }; |
| |
| template <class _Tp, class _Up, class = void> |
| struct __common_type2_imp : __common_type3<_Tp, _Up> {}; |
| #else |
| template <class _Tp, class _Up, class = void> |
| struct __common_type2_imp {}; |
| #endif |
| |
| // sub-bullet 3 - "if decay_t<decltype(false ? declval<D1>() : declval<D2>())> ..." |
| template <class _Tp, class _Up> |
| struct __common_type2_imp<_Tp, _Up, __void_t<decltype(true ? std::declval<_Tp>() : std::declval<_Up>())> > { |
| typedef _LIBCPP_NODEBUG __decay_t<decltype(true ? std::declval<_Tp>() : std::declval<_Up>())> type; |
| }; |
| |
| template <class, class = void> |
| struct __common_type_impl {}; |
| |
| template <class... _Tp> |
| struct __common_types; |
| template <class... _Tp> |
| struct _LIBCPP_TEMPLATE_VIS common_type; |
| |
| template <class _Tp, class _Up> |
| struct __common_type_impl< __common_types<_Tp, _Up>, __void_t<typename common_type<_Tp, _Up>::type> > { |
| typedef typename common_type<_Tp, _Up>::type type; |
| }; |
| |
| template <class _Tp, class _Up, class _Vp, class... _Rest> |
| struct __common_type_impl<__common_types<_Tp, _Up, _Vp, _Rest...>, __void_t<typename common_type<_Tp, _Up>::type> > |
| : __common_type_impl<__common_types<typename common_type<_Tp, _Up>::type, _Vp, _Rest...> > {}; |
| |
| // bullet 1 - sizeof...(Tp) == 0 |
| |
| template <> |
| struct _LIBCPP_TEMPLATE_VIS common_type<> {}; |
| |
| // bullet 2 - sizeof...(Tp) == 1 |
| |
| template <class _Tp> |
| struct _LIBCPP_TEMPLATE_VIS common_type<_Tp> : public common_type<_Tp, _Tp> {}; |
| |
| // bullet 3 - sizeof...(Tp) == 2 |
| |
| // sub-bullet 1 - "If is_same_v<T1, D1> is false or ..." |
| template <class _Tp, class _Up> |
| struct _LIBCPP_TEMPLATE_VIS common_type<_Tp, _Up> |
| : conditional<_IsSame<_Tp, __decay_t<_Tp> >::value && _IsSame<_Up, __decay_t<_Up> >::value, |
| __common_type2_imp<_Tp, _Up>, |
| common_type<__decay_t<_Tp>, __decay_t<_Up> > >::type {}; |
| |
| // bullet 4 - sizeof...(Tp) > 2 |
| |
| template <class _Tp, class _Up, class _Vp, class... _Rest> |
| struct _LIBCPP_TEMPLATE_VIS common_type<_Tp, _Up, _Vp, _Rest...> |
| : __common_type_impl<__common_types<_Tp, _Up, _Vp, _Rest...> > {}; |
| |
| #if _LIBCPP_STD_VER >= 14 |
| template <class... _Tp> |
| using common_type_t = typename common_type<_Tp...>::type; |
| #endif |
| |
| _LIBCPP_END_NAMESPACE_STD |
| |
| #endif // _LIBCPP___TYPE_TRAITS_COMMON_TYPE_H |