libcxx/include/__ranges/reverse_view.h

   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 noexcept(noexcept(reverse_view{
 185       std::forward<_Range>(__range)})) -> decltype(reverse_view{std::forward<_Range>(__range)}) {
 186     return reverse_view{std::forward<_Range>(__range)};
 187   }
 188 };
 189 } // namespace __reverse
 190
 191 inline namespace __cpo {
 192 inline constexpr auto reverse = __reverse::__fn{};
 193 } // namespace __cpo
 194 } // namespace views
 195 } // namespace ranges
 196
 197 #endif // _LIBCPP_STD_VER >= 20
 198
 199 _LIBCPP_END_NAMESPACE_STD
 200
 201 _LIBCPP_POP_MACROS
 202
 203 #endif // _LIBCPP___RANGES_REVERSE_VIEW_H