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_CONJUNCTION_H 10 #define _LIBCPP___TYPE_TRAITS_CONJUNCTION_H 11 12 #include <__config> 13 #include <__type_traits/conditional.h> 14 #include <__type_traits/enable_if.h> 15 #include <__type_traits/integral_constant.h> 16 17 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) 18 # pragma GCC system_header 19 #endif 20 21 _LIBCPP_BEGIN_NAMESPACE_STD 22 23 template <class...> 24 using __expand_to_true = true_type; 25 26 template <class... _Pred> 27 __expand_to_true<__enable_if_t<_Pred::value>...> __and_helper(int); 28 29 template <class...> 30 false_type __and_helper(...); 31 32 // _And always performs lazy evaluation of its arguments. 33 // 34 // However, `_And<_Pred...>` itself will evaluate its result immediately (without having to 35 // be instantiated) since it is an alias, unlike `conjunction<_Pred...>`, which is a struct. 36 // If you want to defer the evaluation of `_And<_Pred...>` itself, use `_Lazy<_And, _Pred...>`. 37 template <class... _Pred> 38 using _And _LIBCPP_NODEBUG = decltype(std::__and_helper<_Pred...>(0)); 39 40 #if _LIBCPP_STD_VER >= 17 41 42 template <class...> 43 struct conjunction : true_type {}; 44 45 template <class _Arg> 46 struct conjunction<_Arg> : _Arg {}; 47 48 template <class _Arg, class... _Args> 49 struct conjunction<_Arg, _Args...> : conditional_t<!bool(_Arg::value), _Arg, conjunction<_Args...>> {}; 50 51 template <class... _Args> 52 inline constexpr bool conjunction_v = conjunction<_Args...>::value; 53 54 #endif // _LIBCPP_STD_VER >= 17 55 56 _LIBCPP_END_NAMESPACE_STD 57 58 #endif // _LIBCPP___TYPE_TRAITS_CONJUNCTION_H 59