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 {typedef _If type;}; 40 template <class _If, class _Then> 41 struct _LIBCPP_TEMPLATE_VIS conditional<false, _If, _Then> {typedef _Then type;}; 42 43 #if _LIBCPP_STD_VER > 11 44 template <bool _Bp, class _IfRes, class _ElseRes> 45 using conditional_t = typename conditional<_Bp, _IfRes, _ElseRes>::type; 46 #endif 47 48 // Helper so we can use "conditional_t" in all language versions. 49 template <bool _Bp, class _If, class _Then> using __conditional_t = typename conditional<_Bp, _If, _Then>::type; 50 51 _LIBCPP_END_NAMESPACE_STD 52 53 #endif // _LIBCPP___TYPE_TRAITS_CONDITIONAL_H 54