libcxx/include/__algorithm/iterator_operations.h

   1 //===----------------------------------------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #ifndef _LIBCPP___ALGORITHM_ITERATOR_OPERATIONS_H
  10 #define _LIBCPP___ALGORITHM_ITERATOR_OPERATIONS_H
  11
  12 #include <__algorithm/iter_swap.h>
  13 #include <__algorithm/ranges_iterator_concept.h>
  14 #include <__assert>
  15 #include <__config>
  16 #include <__iterator/advance.h>
  17 #include <__iterator/distance.h>
  18 #include <__iterator/incrementable_traits.h>
  19 #include <__iterator/iter_move.h>
  20 #include <__iterator/iter_swap.h>
  21 #include <__iterator/iterator_traits.h>
  22 #include <__iterator/next.h>
  23 #include <__iterator/prev.h>
  24 #include <__iterator/readable_traits.h>
  25 #include <__type_traits/enable_if.h>
  26 #include <__type_traits/is_reference.h>
  27 #include <__type_traits/is_same.h>
  28 #include <__type_traits/remove_cvref.h>
  29 #include <__utility/declval.h>
  30 #include <__utility/forward.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 template <class _AlgPolicy>
  43 struct _IterOps;
  44
  45 #if _LIBCPP_STD_VER >= 20
  46 struct _RangeAlgPolicy {};
  47
  48 template <>
  49 struct _IterOps<_RangeAlgPolicy> {
  50   template <class _Iter>
  51   using __value_type = iter_value_t<_Iter>;
  52
  53   template <class _Iter>
  54   using __iterator_category = ranges::__iterator_concept<_Iter>;
  55
  56   template <class _Iter>
  57   using __difference_type = iter_difference_t<_Iter>;
  58
  59   static constexpr auto advance      = ranges::advance;
  60   static constexpr auto distance     = ranges::distance;
  61   static constexpr auto __iter_move  = ranges::iter_move;
  62   static constexpr auto iter_swap    = ranges::iter_swap;
  63   static constexpr auto next         = ranges::next;
  64   static constexpr auto prev         = ranges::prev;
  65   static constexpr auto __advance_to = ranges::advance;
  66 };
  67
  68 #endif
  69
  70 struct _ClassicAlgPolicy {};
  71
  72 template <>
  73 struct _IterOps<_ClassicAlgPolicy> {
  74   template <class _Iter>
  75   using __value_type = typename iterator_traits<_Iter>::value_type;
  76
  77   template <class _Iter>
  78   using __iterator_category = typename iterator_traits<_Iter>::iterator_category;
  79
  80   template <class _Iter>
  81   using __difference_type = typename iterator_traits<_Iter>::difference_type;
  82
  83   // advance
  84   template <class _Iter, class _Distance>
  85   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 static void advance(_Iter& __iter, _Distance __count) {
  86     std::advance(__iter, __count);
  87   }
  88
  89   // distance
  90   template <class _Iter>
  91   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 static typename iterator_traits<_Iter>::difference_type
  92   distance(_Iter __first, _Iter __last) {
  93     return std::distance(__first, __last);
  94   }
  95
  96   template <class _Iter>
  97   using __deref_t = decltype(*std::declval<_Iter&>());
  98
  99   template <class _Iter>
 100   using __move_t = decltype(std::move(*std::declval<_Iter&>()));
 101
 102   template <class _Iter>
 103   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 static void __validate_iter_reference() {
 104     static_assert(
 105         is_same<__deref_t<_Iter>, typename iterator_traits<__remove_cvref_t<_Iter> >::reference>::value,
 106         "It looks like your iterator's `iterator_traits<It>::reference` does not match the return type of "
 107         "dereferencing the iterator, i.e., calling `*it`. This is undefined behavior according to [input.iterators] "
 108         "and can lead to dangling reference issues at runtime, so we are flagging this.");
 109   }
 110
 111   // iter_move
 112   template <class _Iter, __enable_if_t<is_reference<__deref_t<_Iter> >::value, int> = 0>
 113   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 static
 114       // If the result of dereferencing `_Iter` is a reference type, deduce the result of calling `std::move` on it.
 115       // Note that the C++03 mode doesn't support `decltype(auto)` as the return type.
 116       __move_t<_Iter>
 117       __iter_move(_Iter&& __i) {
 118     __validate_iter_reference<_Iter>();
 119
 120     return std::move(*std::forward<_Iter>(__i));
 121   }
 122
 123   template <class _Iter, __enable_if_t<!is_reference<__deref_t<_Iter> >::value, int> = 0>
 124   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 static
 125       // If the result of dereferencing `_Iter` is a value type, deduce the return value of this function to also be a
 126       // value -- otherwise, after `operator*` returns a temporary, this function would return a dangling reference to
 127       // that temporary. Note that the C++03 mode doesn't support `auto` as the return type.
 128       __deref_t<_Iter>
 129       __iter_move(_Iter&& __i) {
 130     __validate_iter_reference<_Iter>();
 131
 132     return *std::forward<_Iter>(__i);
 133   }
 134
 135   // iter_swap
 136   template <class _Iter1, class _Iter2>
 137   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 static void iter_swap(_Iter1&& __a, _Iter2&& __b) {
 138     std::iter_swap(std::forward<_Iter1>(__a), std::forward<_Iter2>(__b));
 139   }
 140
 141   // next
 142   template <class _Iterator>
 143   _LIBCPP_HIDE_FROM_ABI static _LIBCPP_CONSTEXPR_SINCE_CXX14 _Iterator next(_Iterator, _Iterator __last) {
 144     return __last;
 145   }
 146
 147   template <class _Iter>
 148   _LIBCPP_HIDE_FROM_ABI static _LIBCPP_CONSTEXPR_SINCE_CXX14 __remove_cvref_t<_Iter>
 149   next(_Iter&& __it, typename iterator_traits<__remove_cvref_t<_Iter> >::difference_type __n = 1) {
 150     return std::next(std::forward<_Iter>(__it), __n);
 151   }
 152
 153   // prev
 154   template <class _Iter>
 155   _LIBCPP_HIDE_FROM_ABI static _LIBCPP_CONSTEXPR_SINCE_CXX14 __remove_cvref_t<_Iter>
 156   prev(_Iter&& __iter, typename iterator_traits<__remove_cvref_t<_Iter> >::difference_type __n = 1) {
 157     return std::prev(std::forward<_Iter>(__iter), __n);
 158   }
 159
 160   template <class _Iter>
 161   _LIBCPP_HIDE_FROM_ABI static _LIBCPP_CONSTEXPR_SINCE_CXX14 void __advance_to(_Iter& __first, _Iter __last) {
 162     __first = __last;
 163   }
 164
 165   // advance with sentinel, a la std::ranges::advance
 166   template <class _Iter>
 167   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 static __difference_type<_Iter>
 168   __advance_to(_Iter& __iter, __difference_type<_Iter> __count, const _Iter& __sentinel) {
 169     return _IterOps::__advance_to(__iter, __count, __sentinel, typename iterator_traits<_Iter>::iterator_category());
 170   }
 171
 172 private:
 173   // advance with sentinel, a la std::ranges::advance -- InputIterator specialization
 174   template <class _InputIter>
 175   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 static __difference_type<_InputIter> __advance_to(
 176       _InputIter& __iter, __difference_type<_InputIter> __count, const _InputIter& __sentinel, input_iterator_tag) {
 177     __difference_type<_InputIter> __dist = 0;
 178     for (; __dist < __count && __iter != __sentinel; ++__dist)
 179       ++__iter;
 180     return __count - __dist;
 181   }
 182
 183   // advance with sentinel, a la std::ranges::advance -- BidirectionalIterator specialization
 184   template <class _BiDirIter>
 185   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 static __difference_type<_BiDirIter>
 186   __advance_to(_BiDirIter& __iter,
 187                __difference_type<_BiDirIter> __count,
 188                const _BiDirIter& __sentinel,
 189                bidirectional_iterator_tag) {
 190     __difference_type<_BiDirIter> __dist = 0;
 191     if (__count >= 0)
 192       for (; __dist < __count && __iter != __sentinel; ++__dist)
 193         ++__iter;
 194     else
 195       for (__count = -__count; __dist < __count && __iter != __sentinel; ++__dist)
 196         --__iter;
 197     return __count - __dist;
 198   }
 199
 200   // advance with sentinel, a la std::ranges::advance -- RandomIterator specialization
 201   template <class _RandIter>
 202   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 static __difference_type<_RandIter>
 203   __advance_to(_RandIter& __iter,
 204                __difference_type<_RandIter> __count,
 205                const _RandIter& __sentinel,
 206                random_access_iterator_tag) {
 207     auto __dist = _IterOps::distance(__iter, __sentinel);
 208     _LIBCPP_ASSERT_VALID_INPUT_RANGE(
 209         __count == 0 || (__dist < 0) == (__count < 0), "__sentinel must precede __iter when __count < 0");
 210     if (__count < 0)
 211       __dist = __dist > __count ? __dist : __count;
 212     else
 213       __dist = __dist < __count ? __dist : __count;
 214     __iter += __dist;
 215     return __count - __dist;
 216   }
 217 };
 218
 219 template <class _AlgPolicy, class _Iter>
 220 using __policy_iter_diff_t = typename _IterOps<_AlgPolicy>::template __difference_type<_Iter>;
 221
 222 _LIBCPP_END_NAMESPACE_STD
 223
 224 _LIBCPP_POP_MACROS
 225
 226 #endif // _LIBCPP___ALGORITHM_ITERATOR_OPERATIONS_H