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