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_INCREMENTABLE_TRAITS_H
11#define _LIBCPP___ITERATOR_INCREMENTABLE_TRAITS_H
12
13#include <__concepts/arithmetic.h>
14#include <__config>
15#include <__cstddef/ptrdiff_t.h>
16#include <__type_traits/conditional.h>
17#include <__type_traits/is_object.h>
18#include <__type_traits/is_primary_template.h>
19#include <__type_traits/make_signed.h>
20#include <__type_traits/remove_cvref.h>
21#include <__utility/declval.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#if _LIBCPP_STD_VER >= 20
30
31// [incrementable.traits]
32template <class>
33struct incrementable_traits {};
34
35template <class _Tp>
36 requires is_object_v<_Tp>
37struct incrementable_traits<_Tp*> {
38 using difference_type = ptrdiff_t;
39};
40
41template <class _Ip>
42struct incrementable_traits<const _Ip> : incrementable_traits<_Ip> {};
43
44template <class _Tp>
45concept __has_member_difference_type = requires { typename _Tp::difference_type; };
46
47template <__has_member_difference_type _Tp>
48struct incrementable_traits<_Tp> {
49 using difference_type = typename _Tp::difference_type;
50};
51
52template <class _Tp>
53concept __has_integral_minus = requires(const _Tp& __x, const _Tp& __y) {
54 { __x - __y } -> integral;
55};
56
57template <__has_integral_minus _Tp>
58 requires(!__has_member_difference_type<_Tp>)
59struct incrementable_traits<_Tp> {
60 using difference_type = make_signed_t<decltype(std::declval<_Tp>() - std::declval<_Tp>())>;
61};
62
63template <class>
64struct iterator_traits;
65
66// Let `RI` be `remove_cvref_t<I>`. The type `iter_difference_t<I>` denotes
67// `incrementable_traits<RI>::difference_type` if `iterator_traits<RI>` names a specialization
68// generated from the primary template, and `iterator_traits<RI>::difference_type` otherwise.
69template <class _Ip>
70using iter_difference_t =
71 typename conditional_t<__is_primary_template<iterator_traits<remove_cvref_t<_Ip> > >::value,
72 incrementable_traits<remove_cvref_t<_Ip> >,
73 iterator_traits<remove_cvref_t<_Ip> > >::difference_type;
74
75#endif // _LIBCPP_STD_VER >= 20
76
77_LIBCPP_END_NAMESPACE_STD
78
79#endif // _LIBCPP___ITERATOR_INCREMENTABLE_TRAITS_H
80