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_CONDITIONAL_H 10 #define _LIBCPP___TYPE_TRAITS_CONDITIONAL_H 11 12 #include <__config> 13 14 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) 15 # pragma GCC system_header 16 #endif 17 18 _LIBCPP_BEGIN_NAMESPACE_STD 19 20 template <bool> 21 struct _IfImpl; 22 23 template <> 24 struct _IfImpl<true> { 25 template <class _IfRes, class _ElseRes> 26 using _Select _LIBCPP_NODEBUG = _IfRes; 27 }; 28 29 template <> 30 struct _IfImpl<false> { 31 template <class _IfRes, class _ElseRes> 32 using _Select _LIBCPP_NODEBUG = _ElseRes; 33 }; 34 35 template <bool _Cond, class _IfRes, class _ElseRes> 36 using _If _LIBCPP_NODEBUG = typename _IfImpl<_Cond>::template _Select<_IfRes, _ElseRes>; 37 38 template <bool _Bp, class _If, class _Then> 39 struct _LIBCPP_TEMPLATE_VIS conditional { 40 using type _LIBCPP_NODEBUG = _If; 41 }; 42 template <class _If, class _Then> 43 struct _LIBCPP_TEMPLATE_VIS conditional<false, _If, _Then> { 44 using type _LIBCPP_NODEBUG = _Then; 45 }; 46 47 #if _LIBCPP_STD_VER >= 14 48 template <bool _Bp, class _IfRes, class _ElseRes> 49 using conditional_t _LIBCPP_NODEBUG = typename conditional<_Bp, _IfRes, _ElseRes>::type; 50 #endif 51 52 // Helper so we can use "conditional_t" in all language versions. 53 template <bool _Bp, class _If, class _Then> 54 using __conditional_t _LIBCPP_NODEBUG = typename conditional<_Bp, _If, _Then>::type; 55 56 _LIBCPP_END_NAMESPACE_STD 57 58 #endif // _LIBCPP___TYPE_TRAITS_CONDITIONAL_H 59