1 // -*- C++ -*- 2 //===----------------------------------------------------------------------===// 3 // 4 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 5 // See https://llvm.org/LICENSE.txt for license information. 6 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 7 // 8 //===----------------------------------------------------------------------===// 9 10 #ifndef _LIBCPP___RANGES_EMPTY_H 11 #define _LIBCPP___RANGES_EMPTY_H 12 13 #include <__concepts/class_or_enum.h> 14 #include <__config> 15 #include <__iterator/concepts.h> 16 #include <__ranges/access.h> 17 #include <__ranges/size.h> 18 19 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) 20 # pragma GCC system_header 21 #endif 22 23 _LIBCPP_BEGIN_NAMESPACE_STD 24 25 #if _LIBCPP_STD_VER >= 20 26 27 // [range.prim.empty] 28 29 namespace ranges { 30 namespace __empty { 31 template <class _Tp> 32 concept __member_empty = __workaround_52970<_Tp> && requires(_Tp&& __t) { bool(__t.empty()); }; 33 34 template <class _Tp> 35 concept __can_invoke_size = !__member_empty<_Tp> && requires(_Tp&& __t) { ranges::size(__t); }; 36 37 template <class _Tp> 38 concept __can_compare_begin_end = !__member_empty<_Tp> && !__can_invoke_size<_Tp> && requires(_Tp&& __t) { 39 bool(ranges::begin(__t) == ranges::end(__t)); 40 { ranges::begin(__t) } -> forward_iterator; 41 }; 42 43 struct __fn { 44 template <__member_empty _Tp> 45 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr bool operator()(_Tp&& __t) const noexcept(noexcept(bool(__t.empty()))) { 46 return bool(__t.empty()); 47 } 48 49 template <__can_invoke_size _Tp> 50 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr bool operator()(_Tp&& __t) const noexcept(noexcept(ranges::size(__t))) { 51 return ranges::size(__t) == 0; 52 } 53 54 template <__can_compare_begin_end _Tp> 55 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr bool operator()(_Tp&& __t) const 56 noexcept(noexcept(bool(ranges::begin(__t) == ranges::end(__t)))) { 57 return ranges::begin(__t) == ranges::end(__t); 58 } 59 }; 60 } // namespace __empty 61 62 inline namespace __cpo { 63 inline constexpr auto empty = __empty::__fn{}; 64 } // namespace __cpo 65 } // namespace ranges 66 67 #endif // _LIBCPP_STD_VER >= 20 68 69 _LIBCPP_END_NAMESPACE_STD 70 71 #endif // _LIBCPP___RANGES_EMPTY_H 72