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 <__config>
14 #include <__type_traits/is_primary_template.h>
15 #include <concepts>
16 #include <type_traits>
17 
18 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
19 #  pragma GCC system_header
20 #endif
21 
22 _LIBCPP_BEGIN_NAMESPACE_STD
23 
24 #if _LIBCPP_STD_VER > 17
25 
26 // [incrementable.traits]
27 template<class> struct incrementable_traits {};
28 
29 template<class _Tp>
30 requires is_object_v<_Tp>
31 struct incrementable_traits<_Tp*> {
32   using difference_type = ptrdiff_t;
33 };
34 
35 template<class _Ip>
36 struct incrementable_traits<const _Ip> : incrementable_traits<_Ip> {};
37 
38 template<class _Tp>
39 concept __has_member_difference_type = requires { typename _Tp::difference_type; };
40 
41 template<__has_member_difference_type _Tp>
42 struct incrementable_traits<_Tp> {
43   using difference_type = typename _Tp::difference_type;
44 };
45 
46 template<class _Tp>
47 concept __has_integral_minus =
48   requires(const _Tp& __x, const _Tp& __y) {
49     { __x - __y } -> integral;
50   };
51 
52 template<__has_integral_minus _Tp>
53 requires (!__has_member_difference_type<_Tp>)
54 struct incrementable_traits<_Tp> {
55   using difference_type = make_signed_t<decltype(declval<_Tp>() - declval<_Tp>())>;
56 };
57 
58 template <class>
59 struct iterator_traits;
60 
61 // Let `RI` be `remove_cvref_t<I>`. The type `iter_difference_t<I>` denotes
62 // `incrementable_traits<RI>::difference_type` if `iterator_traits<RI>` names a specialization
63 // generated from the primary template, and `iterator_traits<RI>::difference_type` otherwise.
64 template <class _Ip>
65 using iter_difference_t = typename conditional_t<__is_primary_template<iterator_traits<remove_cvref_t<_Ip> > >::value,
66                                                  incrementable_traits<remove_cvref_t<_Ip> >,
67                                                  iterator_traits<remove_cvref_t<_Ip> > >::difference_type;
68 
69 #endif // _LIBCPP_STD_VER > 17
70 
71 _LIBCPP_END_NAMESPACE_STD
72 
73 #endif // _LIBCPP___ITERATOR_INCREMENTABLE_TRAITS_H
74