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