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_REVERSE_VIEW_H
11 #define _LIBCPP___RANGES_REVERSE_VIEW_H
12 
13 #include <__concepts/constructible.h>
14 #include <__config>
15 #include <__iterator/concepts.h>
16 #include <__iterator/next.h>
17 #include <__iterator/reverse_iterator.h>
18 #include <__ranges/access.h>
19 #include <__ranges/all.h>
20 #include <__ranges/concepts.h>
21 #include <__ranges/enable_borrowed_range.h>
22 #include <__ranges/non_propagating_cache.h>
23 #include <__ranges/range_adaptor.h>
24 #include <__ranges/size.h>
25 #include <__ranges/subrange.h>
26 #include <__ranges/view_interface.h>
27 #include <__type_traits/conditional.h>
28 #include <__type_traits/remove_cvref.h>
29 #include <__utility/forward.h>
30 #include <__utility/move.h>
31 
32 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
33 #  pragma GCC system_header
34 #endif
35 
36 _LIBCPP_PUSH_MACROS
37 #include <__undef_macros>
38 
39 _LIBCPP_BEGIN_NAMESPACE_STD
40 
41 #if _LIBCPP_STD_VER >= 20
42 
43 namespace ranges {
44 template <view _View>
45   requires bidirectional_range<_View>
46 class reverse_view : public view_interface<reverse_view<_View>> {
47   // We cache begin() whenever ranges::next is not guaranteed O(1) to provide an
48   // amortized O(1) begin() method.
49   static constexpr bool _UseCache = !random_access_range<_View> && !common_range<_View>;
50   using _Cache = _If<_UseCache, __non_propagating_cache<reverse_iterator<iterator_t<_View>>>, __empty_cache>;
51   _LIBCPP_NO_UNIQUE_ADDRESS _Cache __cached_begin_ = _Cache();
52   _LIBCPP_NO_UNIQUE_ADDRESS _View __base_          = _View();
53 
54 public:
55   _LIBCPP_HIDE_FROM_ABI reverse_view()
56     requires default_initializable<_View>
57   = default;
58 
59   _LIBCPP_HIDE_FROM_ABI constexpr explicit reverse_view(_View __view) : __base_(std::move(__view)) {}
60 
61   _LIBCPP_HIDE_FROM_ABI constexpr _View base() const&
62     requires copy_constructible<_View>
63   {
64     return __base_;
65   }
66 
67   _LIBCPP_HIDE_FROM_ABI constexpr _View base() && { return std::move(__base_); }
68 
69   _LIBCPP_HIDE_FROM_ABI constexpr reverse_iterator<iterator_t<_View>> begin() {
70     if constexpr (_UseCache)
71       if (__cached_begin_.__has_value())
72         return *__cached_begin_;
73 
74     auto __tmp = std::make_reverse_iterator(ranges::next(ranges::begin(__base_), ranges::end(__base_)));
75     if constexpr (_UseCache)
76       __cached_begin_.__emplace(__tmp);
77     return __tmp;
78   }
79 
80   _LIBCPP_HIDE_FROM_ABI constexpr reverse_iterator<iterator_t<_View>> begin()
81     requires common_range<_View>
82   {
83     return std::make_reverse_iterator(ranges::end(__base_));
84   }
85 
86   _LIBCPP_HIDE_FROM_ABI constexpr auto begin() const
87     requires common_range<const _View>
88   {
89     return std::make_reverse_iterator(ranges::end(__base_));
90   }
91 
92   _LIBCPP_HIDE_FROM_ABI constexpr reverse_iterator<iterator_t<_View>> end() {
93     return std::make_reverse_iterator(ranges::begin(__base_));
94   }
95 
96   _LIBCPP_HIDE_FROM_ABI constexpr auto end() const
97     requires common_range<const _View>
98   {
99     return std::make_reverse_iterator(ranges::begin(__base_));
100   }
101 
102   _LIBCPP_HIDE_FROM_ABI constexpr auto size()
103     requires sized_range<_View>
104   {
105     return ranges::size(__base_);
106   }
107 
108   _LIBCPP_HIDE_FROM_ABI constexpr auto size() const
109     requires sized_range<const _View>
110   {
111     return ranges::size(__base_);
112   }
113 };
114 
115 template <class _Range>
116 reverse_view(_Range&&) -> reverse_view<views::all_t<_Range>>;
117 
118 template <class _Tp>
119 inline constexpr bool enable_borrowed_range<reverse_view<_Tp>> = enable_borrowed_range<_Tp>;
120 
121 namespace views {
122 namespace __reverse {
123 template <class _Tp>
124 inline constexpr bool __is_reverse_view = false;
125 
126 template <class _Tp>
127 inline constexpr bool __is_reverse_view<reverse_view<_Tp>> = true;
128 
129 template <class _Tp>
130 inline constexpr bool __is_sized_reverse_subrange = false;
131 
132 template <class _Iter>
133 inline constexpr bool
134     __is_sized_reverse_subrange<subrange<reverse_iterator<_Iter>, reverse_iterator<_Iter>, subrange_kind::sized>> =
135         true;
136 
137 template <class _Tp>
138 inline constexpr bool __is_unsized_reverse_subrange = false;
139 
140 template <class _Iter, subrange_kind _Kind>
141 inline constexpr bool __is_unsized_reverse_subrange<subrange<reverse_iterator<_Iter>, reverse_iterator<_Iter>, _Kind>> =
142     _Kind == subrange_kind::unsized;
143 
144 template <class _Tp>
145 struct __unwrapped_reverse_subrange {
146   using type =
147       void; // avoid SFINAE-ing out the overload below -- let the concept requirements do it for better diagnostics
148 };
149 
150 template <class _Iter, subrange_kind _Kind>
151 struct __unwrapped_reverse_subrange<subrange<reverse_iterator<_Iter>, reverse_iterator<_Iter>, _Kind>> {
152   using type = subrange<_Iter, _Iter, _Kind>;
153 };
154 
155 struct __fn : __range_adaptor_closure<__fn> {
156   template <class _Range>
157     requires __is_reverse_view<remove_cvref_t<_Range>>
158   [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Range&& __range) const
159       noexcept(noexcept(std::forward<_Range>(__range).base())) -> decltype(std::forward<_Range>(__range).base()) {
160     return std::forward<_Range>(__range).base();
161   }
162 
163   template <class _Range,
164             class _UnwrappedSubrange = typename __unwrapped_reverse_subrange<remove_cvref_t<_Range>>::type>
165     requires __is_sized_reverse_subrange<remove_cvref_t<_Range>>
166   [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Range&& __range) const
167       noexcept(noexcept(_UnwrappedSubrange(__range.end().base(), __range.begin().base(), __range.size())))
168           -> decltype(_UnwrappedSubrange(__range.end().base(), __range.begin().base(), __range.size())) {
169     return _UnwrappedSubrange(__range.end().base(), __range.begin().base(), __range.size());
170   }
171 
172   template <class _Range,
173             class _UnwrappedSubrange = typename __unwrapped_reverse_subrange<remove_cvref_t<_Range>>::type>
174     requires __is_unsized_reverse_subrange<remove_cvref_t<_Range>>
175   [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Range&& __range) const
176       noexcept(noexcept(_UnwrappedSubrange(__range.end().base(), __range.begin().base())))
177           -> decltype(_UnwrappedSubrange(__range.end().base(), __range.begin().base())) {
178     return _UnwrappedSubrange(__range.end().base(), __range.begin().base());
179   }
180 
181   template <class _Range>
182     requires(!__is_reverse_view<remove_cvref_t<_Range>> && !__is_sized_reverse_subrange<remove_cvref_t<_Range>> &&
183              !__is_unsized_reverse_subrange<remove_cvref_t<_Range>>)
184   [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Range&& __range) const
185       noexcept(noexcept(reverse_view{std::forward<_Range>(__range)}))
186           -> decltype(reverse_view{std::forward<_Range>(__range)}) {
187     return reverse_view{std::forward<_Range>(__range)};
188   }
189 };
190 } // namespace __reverse
191 
192 inline namespace __cpo {
193 inline constexpr auto reverse = __reverse::__fn{};
194 } // namespace __cpo
195 } // namespace views
196 } // namespace ranges
197 
198 #endif // _LIBCPP_STD_VER >= 20
199 
200 _LIBCPP_END_NAMESPACE_STD
201 
202 _LIBCPP_POP_MACROS
203 
204 #endif // _LIBCPP___RANGES_REVERSE_VIEW_H
205