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 = 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