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
29template <class _InputIter>
30inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 typename iterator_traits<_InputIter>::difference_type
31__distance(_InputIter __first, _InputIter __last, input_iterator_tag) {
32  typename iterator_traits<_InputIter>::difference_type __r(0);
33  for (; __first != __last; ++__first)
34    ++__r;
35  return __r;
36}
37
38template <class _RandIter>
39inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 typename iterator_traits<_RandIter>::difference_type
40__distance(_RandIter __first, _RandIter __last, random_access_iterator_tag) {
41  return __last - __first;
42}
43
44template <class _InputIter>
45inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 typename iterator_traits<_InputIter>::difference_type
46distance(_InputIter __first, _InputIter __last) {
47  return std::__distance(__first, __last, typename iterator_traits<_InputIter>::iterator_category());
48}
49
50#if _LIBCPP_STD_VER >= 20
51
52// [range.iter.op.distance]
53
54namespace ranges {
55namespace __distance {
56
57struct __fn {
58  template <class _Ip, sentinel_for<_Ip> _Sp>
59    requires(!sized_sentinel_for<_Sp, _Ip>)
60  _LIBCPP_HIDE_FROM_ABI constexpr iter_difference_t<_Ip> operator()(_Ip __first, _Sp __last) const {
61    iter_difference_t<_Ip> __n = 0;
62    while (__first != __last) {
63      ++__first;
64      ++__n;
65    }
66    return __n;
67  }
68
69  template <class _Ip, sized_sentinel_for<decay_t<_Ip>> _Sp>
70  _LIBCPP_HIDE_FROM_ABI constexpr iter_difference_t<_Ip> operator()(_Ip&& __first, _Sp __last) const {
71    if constexpr (sized_sentinel_for<_Sp, __remove_cvref_t<_Ip>>) {
72      return __last - __first;
73    } else {
74      return __last - decay_t<_Ip>(__first);
75    }
76  }
77
78  template <range _Rp>
79  _LIBCPP_HIDE_FROM_ABI constexpr range_difference_t<_Rp> operator()(_Rp&& __r) const {
80    if constexpr (sized_range<_Rp>) {
81      return static_cast<range_difference_t<_Rp>>(ranges::size(__r));
82    } else {
83      return operator()(ranges::begin(__r), ranges::end(__r));
84    }
85  }
86};
87
88} // namespace __distance
89
90inline namespace __cpo {
91inline constexpr auto distance = __distance::__fn{};
92} // namespace __cpo
93} // namespace ranges
94
95#endif // _LIBCPP_STD_VER >= 20
96
97_LIBCPP_END_NAMESPACE_STD
98
99#endif // _LIBCPP___ITERATOR_DISTANCE_H
100