libcxx/include/__iterator/counted_iterator.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___ITERATOR_COUNTED_ITERATOR_H
  11 #define _LIBCPP___ITERATOR_COUNTED_ITERATOR_H
  12
  13 #include <__assert>
  14 #include <__compare/ordering.h>
  15 #include <__concepts/assignable.h>
  16 #include <__concepts/common_with.h>
  17 #include <__concepts/constructible.h>
  18 #include <__concepts/convertible_to.h>
  19 #include <__concepts/same_as.h>
  20 #include <__config>
  21 #include <__iterator/concepts.h>
  22 #include <__iterator/default_sentinel.h>
  23 #include <__iterator/incrementable_traits.h>
  24 #include <__iterator/iter_move.h>
  25 #include <__iterator/iter_swap.h>
  26 #include <__iterator/iterator_traits.h>
  27 #include <__iterator/readable_traits.h>
  28 #include <__memory/pointer_traits.h>
  29 #include <__type_traits/add_pointer.h>
  30 #include <__type_traits/conditional.h>
  31 #include <__utility/move.h>
  32
  33 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  34 #  pragma GCC system_header
  35 #endif
  36
  37 _LIBCPP_PUSH_MACROS
  38 #include <__undef_macros>
  39
  40 _LIBCPP_BEGIN_NAMESPACE_STD
  41
  42 #if _LIBCPP_STD_VER >= 20
  43
  44 template <class>
  45 struct __counted_iterator_concept {};
  46
  47 template <class _Iter>
  48   requires requires { typename _Iter::iterator_concept; }
  49 struct __counted_iterator_concept<_Iter> {
  50   using iterator_concept = typename _Iter::iterator_concept;
  51 };
  52
  53 template <class>
  54 struct __counted_iterator_category {};
  55
  56 template <class _Iter>
  57   requires requires { typename _Iter::iterator_category; }
  58 struct __counted_iterator_category<_Iter> {
  59   using iterator_category = typename _Iter::iterator_category;
  60 };
  61
  62 template <class>
  63 struct __counted_iterator_value_type {};
  64
  65 template <indirectly_readable _Iter>
  66 struct __counted_iterator_value_type<_Iter> {
  67   using value_type = iter_value_t<_Iter>;
  68 };
  69
  70 template <input_or_output_iterator _Iter>
  71 class counted_iterator
  72     : public __counted_iterator_concept<_Iter>,
  73       public __counted_iterator_category<_Iter>,
  74       public __counted_iterator_value_type<_Iter> {
  75 public:
  76   using iterator_type   = _Iter;
  77   using difference_type = iter_difference_t<_Iter>;
  78
  79   _LIBCPP_HIDE_FROM_ABI constexpr counted_iterator()
  80     requires default_initializable<_Iter>
  81   = default;
  82
  83   _LIBCPP_HIDE_FROM_ABI constexpr counted_iterator(_Iter __iter, iter_difference_t<_Iter> __n)
  84       : __current_(std::move(__iter)), __count_(__n) {
  85     _LIBCPP_ASSERT_UNCATEGORIZED(__n >= 0, "__n must not be negative.");
  86   }
  87
  88   template <class _I2>
  89     requires convertible_to<const _I2&, _Iter>
  90   _LIBCPP_HIDE_FROM_ABI constexpr counted_iterator(const counted_iterator<_I2>& __other)
  91       : __current_(__other.__current_), __count_(__other.__count_) {}
  92
  93   template <class _I2>
  94     requires assignable_from<_Iter&, const _I2&>
  95   _LIBCPP_HIDE_FROM_ABI constexpr counted_iterator& operator=(const counted_iterator<_I2>& __other) {
  96     __current_ = __other.__current_;
  97     __count_   = __other.__count_;
  98     return *this;
  99   }
 100
 101   _LIBCPP_HIDE_FROM_ABI constexpr const _Iter& base() const& noexcept { return __current_; }
 102
 103   _LIBCPP_HIDE_FROM_ABI constexpr _Iter base() && { return std::move(__current_); }
 104
 105   _LIBCPP_HIDE_FROM_ABI constexpr iter_difference_t<_Iter> count() const noexcept { return __count_; }
 106
 107   _LIBCPP_HIDE_FROM_ABI constexpr decltype(auto) operator*() {
 108     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(__count_ > 0, "Iterator is equal to or past end.");
 109     return *__current_;
 110   }
 111
 112   _LIBCPP_HIDE_FROM_ABI constexpr decltype(auto) operator*() const
 113     requires __dereferenceable<const _Iter>
 114   {
 115     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(__count_ > 0, "Iterator is equal to or past end.");
 116     return *__current_;
 117   }
 118
 119   _LIBCPP_HIDE_FROM_ABI constexpr auto operator->() const noexcept
 120     requires contiguous_iterator<_Iter>
 121   {
 122     return std::to_address(__current_);
 123   }
 124
 125   _LIBCPP_HIDE_FROM_ABI constexpr counted_iterator& operator++() {
 126     _LIBCPP_ASSERT_UNCATEGORIZED(__count_ > 0, "Iterator already at or past end.");
 127     ++__current_;
 128     --__count_;
 129     return *this;
 130   }
 131
 132   _LIBCPP_HIDE_FROM_ABI constexpr decltype(auto) operator++(int) {
 133     _LIBCPP_ASSERT_UNCATEGORIZED(__count_ > 0, "Iterator already at or past end.");
 134     --__count_;
 135 #  if _LIBCPP_HAS_EXCEPTIONS
 136     try {
 137       return __current_++;
 138     } catch (...) {
 139       ++__count_;
 140       throw;
 141     }
 142 #  else
 143     return __current_++;
 144 #  endif // _LIBCPP_HAS_EXCEPTIONS
 145   }
 146
 147   _LIBCPP_HIDE_FROM_ABI constexpr counted_iterator operator++(int)
 148     requires forward_iterator<_Iter>
 149   {
 150     _LIBCPP_ASSERT_UNCATEGORIZED(__count_ > 0, "Iterator already at or past end.");
 151     counted_iterator __tmp = *this;
 152     ++*this;
 153     return __tmp;
 154   }
 155
 156   _LIBCPP_HIDE_FROM_ABI constexpr counted_iterator& operator--()
 157     requires bidirectional_iterator<_Iter>
 158   {
 159     --__current_;
 160     ++__count_;
 161     return *this;
 162   }
 163
 164   _LIBCPP_HIDE_FROM_ABI constexpr counted_iterator operator--(int)
 165     requires bidirectional_iterator<_Iter>
 166   {
 167     counted_iterator __tmp = *this;
 168     --*this;
 169     return __tmp;
 170   }
 171
 172   _LIBCPP_HIDE_FROM_ABI constexpr counted_iterator operator+(iter_difference_t<_Iter> __n) const
 173     requires random_access_iterator<_Iter>
 174   {
 175     return counted_iterator(__current_ + __n, __count_ - __n);
 176   }
 177
 178   _LIBCPP_HIDE_FROM_ABI friend constexpr counted_iterator
 179   operator+(iter_difference_t<_Iter> __n, const counted_iterator& __x)
 180     requires random_access_iterator<_Iter>
 181   {
 182     return __x + __n;
 183   }
 184
 185   _LIBCPP_HIDE_FROM_ABI constexpr counted_iterator& operator+=(iter_difference_t<_Iter> __n)
 186     requires random_access_iterator<_Iter>
 187   {
 188     _LIBCPP_ASSERT_UNCATEGORIZED(__n <= __count_, "Cannot advance iterator past end.");
 189     __current_ += __n;
 190     __count_ -= __n;
 191     return *this;
 192   }
 193
 194   _LIBCPP_HIDE_FROM_ABI constexpr counted_iterator operator-(iter_difference_t<_Iter> __n) const
 195     requires random_access_iterator<_Iter>
 196   {
 197     return counted_iterator(__current_ - __n, __count_ + __n);
 198   }
 199
 200   template <common_with<_Iter> _I2>
 201   _LIBCPP_HIDE_FROM_ABI friend constexpr iter_difference_t<_I2>
 202   operator-(const counted_iterator& __lhs, const counted_iterator<_I2>& __rhs) {
 203     return __rhs.__count_ - __lhs.__count_;
 204   }
 205
 206   _LIBCPP_HIDE_FROM_ABI friend constexpr iter_difference_t<_Iter>
 207   operator-(const counted_iterator& __lhs, default_sentinel_t) {
 208     return -__lhs.__count_;
 209   }
 210
 211   _LIBCPP_HIDE_FROM_ABI friend constexpr iter_difference_t<_Iter>
 212   operator-(default_sentinel_t, const counted_iterator& __rhs) {
 213     return __rhs.__count_;
 214   }
 215
 216   _LIBCPP_HIDE_FROM_ABI constexpr counted_iterator& operator-=(iter_difference_t<_Iter> __n)
 217     requires random_access_iterator<_Iter>
 218   {
 219     _LIBCPP_ASSERT_UNCATEGORIZED(
 220         -__n <= __count_,
 221         "Attempt to subtract too large of a size: "
 222         "counted_iterator would be decremented before the "
 223         "first element of its range.");
 224     __current_ -= __n;
 225     __count_ += __n;
 226     return *this;
 227   }
 228
 229   _LIBCPP_HIDE_FROM_ABI constexpr decltype(auto) operator[](iter_difference_t<_Iter> __n) const
 230     requires random_access_iterator<_Iter>
 231   {
 232     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(__n < __count_, "Subscript argument must be less than size.");
 233     return __current_[__n];
 234   }
 235
 236   template <common_with<_Iter> _I2>
 237   _LIBCPP_HIDE_FROM_ABI friend constexpr bool
 238   operator==(const counted_iterator& __lhs, const counted_iterator<_I2>& __rhs) {
 239     return __lhs.__count_ == __rhs.__count_;
 240   }
 241
 242   _LIBCPP_HIDE_FROM_ABI friend constexpr bool operator==(const counted_iterator& __lhs, default_sentinel_t) {
 243     return __lhs.__count_ == 0;
 244   }
 245
 246   template <common_with<_Iter> _I2>
 247   _LIBCPP_HIDE_FROM_ABI friend constexpr strong_ordering
 248   operator<=>(const counted_iterator& __lhs, const counted_iterator<_I2>& __rhs) {
 249     return __rhs.__count_ <=> __lhs.__count_;
 250   }
 251
 252   _LIBCPP_HIDE_FROM_ABI friend constexpr decltype(auto)
 253   iter_move(const counted_iterator& __i) noexcept(noexcept(ranges::iter_move(__i.__current_)))
 254     requires input_iterator<_Iter>
 255   {
 256     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(__i.__count_ > 0, "Iterator must not be past end of range.");
 257     return ranges::iter_move(__i.__current_);
 258   }
 259
 260   template <indirectly_swappable<_Iter> _I2>
 261   _LIBCPP_HIDE_FROM_ABI friend constexpr void
 262   iter_swap(const counted_iterator& __x,
 263             const counted_iterator<_I2>& __y) noexcept(noexcept(ranges::iter_swap(__x.__current_, __y.__current_))) {
 264     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
 265         __x.__count_ > 0 && __y.__count_ > 0, "Iterators must not be past end of range.");
 266     return ranges::iter_swap(__x.__current_, __y.__current_);
 267   }
 268
 269 private:
 270   _LIBCPP_NO_UNIQUE_ADDRESS _Iter __current_ = _Iter();
 271   iter_difference_t<_Iter> __count_          = 0;
 272   template <input_or_output_iterator _OtherIter>
 273   friend class counted_iterator;
 274 };
 275 _LIBCPP_CTAD_SUPPORTED_FOR_TYPE(counted_iterator);
 276
 277 template <input_iterator _Iter>
 278   requires same_as<_ITER_TRAITS<_Iter>, iterator_traits<_Iter>>
 279 struct iterator_traits<counted_iterator<_Iter>> : iterator_traits<_Iter> {
 280   using pointer = conditional_t<contiguous_iterator<_Iter>, add_pointer_t<iter_reference_t<_Iter>>, void>;
 281 };
 282
 283 #endif // _LIBCPP_STD_VER >= 20
 284
 285 _LIBCPP_END_NAMESPACE_STD
 286
 287 _LIBCPP_POP_MACROS
 288
 289 #endif // _LIBCPP___ITERATOR_COUNTED_ITERATOR_H