libcxx/include/__iterator/distance.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_DISTANCE_H
  11 #define _LIBCPP___ITERATOR_DISTANCE_H
  12
  13 #include <__config>
  14 #include <__iterator/concepts.h>
  15 #include <__iterator/incrementable_traits.h>
  16 #include <__iterator/iterator_traits.h>
  17 #include <__ranges/access.h>
  18 #include <__ranges/concepts.h>
  19 #include <__ranges/size.h>
  20 #include <__type_traits/decay.h>
  21 #include <__type_traits/remove_cvref.h>
  22
  23 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  24 #  pragma GCC system_header
  25 #endif
  26
  27 _LIBCPP_BEGIN_NAMESPACE_STD
  28
  29 template <class _InputIter>
  30 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX17
  31 typename iterator_traits<_InputIter>::difference_type
  32 __distance(_InputIter __first, _InputIter __last, input_iterator_tag)
  33 {
  34     typename iterator_traits<_InputIter>::difference_type __r(0);
  35     for (; __first != __last; ++__first)
  36         ++__r;
  37     return __r;
  38 }
  39
  40 template <class _RandIter>
  41 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX17
  42 typename iterator_traits<_RandIter>::difference_type
  43 __distance(_RandIter __first, _RandIter __last, random_access_iterator_tag)
  44 {
  45     return __last - __first;
  46 }
  47
  48 template <class _InputIter>
  49 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX17
  50 typename iterator_traits<_InputIter>::difference_type
  51 distance(_InputIter __first, _InputIter __last)
  52 {
  53     return _VSTD::__distance(__first, __last, typename iterator_traits<_InputIter>::iterator_category());
  54 }
  55
  56 #if _LIBCPP_STD_VER >= 20
  57
  58 // [range.iter.op.distance]
  59
  60 namespace ranges {
  61 namespace __distance {
  62
  63 struct __fn {
  64   template<class _Ip, sentinel_for<_Ip> _Sp>
  65     requires (!sized_sentinel_for<_Sp, _Ip>)
  66   _LIBCPP_HIDE_FROM_ABI
  67   constexpr iter_difference_t<_Ip> operator()(_Ip __first, _Sp __last) const {
  68     iter_difference_t<_Ip> __n = 0;
  69     while (__first != __last) {
  70       ++__first;
  71       ++__n;
  72     }
  73     return __n;
  74   }
  75
  76   template<class _Ip, sized_sentinel_for<decay_t<_Ip>> _Sp>
  77   _LIBCPP_HIDE_FROM_ABI
  78   constexpr iter_difference_t<_Ip> operator()(_Ip&& __first, _Sp __last) const {
  79     if constexpr (sized_sentinel_for<_Sp, __remove_cvref_t<_Ip>>) {
  80       return __last - __first;
  81     } else {
  82       return __last - decay_t<_Ip>(__first);
  83     }
  84   }
  85
  86   template<range _Rp>
  87   _LIBCPP_HIDE_FROM_ABI
  88   constexpr range_difference_t<_Rp> operator()(_Rp&& __r) const {
  89     if constexpr (sized_range<_Rp>) {
  90       return static_cast<range_difference_t<_Rp>>(ranges::size(__r));
  91     } else {
  92       return operator()(ranges::begin(__r), ranges::end(__r));
  93     }
  94   }
  95 };
  96
  97 } // namespace __distance
  98
  99 inline namespace __cpo {
 100   inline constexpr auto distance = __distance::__fn{};
 101 } // namespace __cpo
 102 } // namespace ranges
 103
 104 #endif // _LIBCPP_STD_VER >= 20
 105
 106 _LIBCPP_END_NAMESPACE_STD
 107
 108 #endif // _LIBCPP___ITERATOR_DISTANCE_H