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 29namespace ranges { 30namespace __empty { 31template <class _Tp> 32concept __member_empty = __workaround_52970<_Tp> && requires(_Tp&& __t) { bool(__t.empty()); }; 33 34template <class _Tp> 35concept __can_invoke_size = !__member_empty<_Tp> && requires(_Tp&& __t) { ranges::size(__t); }; 36 37template <class _Tp> 38concept __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 43struct __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 62inline namespace __cpo { 63inline 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