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
109