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>
21 
22 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
23 #  pragma GCC system_header
24 #endif
25 
26 _LIBCPP_BEGIN_NAMESPACE_STD
27 
28 template <class _InputIter>
29 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
30 typename iterator_traits<_InputIter>::difference_type
31 __distance(_InputIter __first, _InputIter __last, input_iterator_tag)
32 {
33     typename iterator_traits<_InputIter>::difference_type __r(0);
34     for (; __first != __last; ++__first)
35         ++__r;
36     return __r;
37 }
38 
39 template <class _RandIter>
40 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
41 typename iterator_traits<_RandIter>::difference_type
42 __distance(_RandIter __first, _RandIter __last, random_access_iterator_tag)
43 {
44     return __last - __first;
45 }
46 
47 template <class _InputIter>
48 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
49 typename iterator_traits<_InputIter>::difference_type
50 distance(_InputIter __first, _InputIter __last)
51 {
52     return _VSTD::__distance(__first, __last, typename iterator_traits<_InputIter>::iterator_category());
53 }
54 
55 #if _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_INCOMPLETE_RANGES)
56 
57 // [range.iter.op.distance]
58 
59 namespace ranges {
60 namespace __distance {
61 
62 struct __fn {
63   template<class _Ip, sentinel_for<_Ip> _Sp>
64     requires (!sized_sentinel_for<_Sp, _Ip>)
65   _LIBCPP_HIDE_FROM_ABI
66   constexpr iter_difference_t<_Ip> operator()(_Ip __first, _Sp __last) const {
67     iter_difference_t<_Ip> __n = 0;
68     while (__first != __last) {
69       ++__first;
70       ++__n;
71     }
72     return __n;
73   }
74 
75   template<class _Ip, sized_sentinel_for<decay_t<_Ip>> _Sp>
76   _LIBCPP_HIDE_FROM_ABI
77   constexpr iter_difference_t<_Ip> operator()(_Ip&& __first, _Sp __last) const {
78     if constexpr (sized_sentinel_for<_Sp, __uncvref_t<_Ip>>) {
79       return __last - __first;
80     } else {
81       return __last - decay_t<_Ip>(__first);
82     }
83   }
84 
85   template<range _Rp>
86   _LIBCPP_HIDE_FROM_ABI
87   constexpr range_difference_t<_Rp> operator()(_Rp&& __r) const {
88     if constexpr (sized_range<_Rp>) {
89       return static_cast<range_difference_t<_Rp>>(ranges::size(__r));
90     } else {
91       return operator()(ranges::begin(__r), ranges::end(__r));
92     }
93   }
94 };
95 
96 } // namespace __distance
97 
98 inline namespace __cpo {
99   inline constexpr auto distance = __distance::__fn{};
100 } // namespace __cpo
101 } // namespace ranges
102 
103 #endif // _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_INCOMPLETE_RANGES)
104 
105 _LIBCPP_END_NAMESPACE_STD
106 
107 #endif // _LIBCPP___ITERATOR_DISTANCE_H
108