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