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 <cstddef>
17 #include <type_traits>
18 
19 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
20 #  pragma GCC system_header
21 #endif
22 
23 _LIBCPP_BEGIN_NAMESPACE_STD
24 
25 #if _LIBCPP_STD_VER > 17
26 
27 // [incrementable.traits]
28 template<class> struct incrementable_traits {};
29 
30 template<class _Tp>
31 requires is_object_v<_Tp>
32 struct incrementable_traits<_Tp*> {
33   using difference_type = ptrdiff_t;
34 };
35 
36 template<class _Ip>
37 struct incrementable_traits<const _Ip> : incrementable_traits<_Ip> {};
38 
39 template<class _Tp>
40 concept __has_member_difference_type = requires { typename _Tp::difference_type; };
41 
42 template<__has_member_difference_type _Tp>
43 struct incrementable_traits<_Tp> {
44   using difference_type = typename _Tp::difference_type;
45 };
46 
47 template<class _Tp>
48 concept __has_integral_minus =
49   requires(const _Tp& __x, const _Tp& __y) {
50     { __x - __y } -> integral;
51   };
52 
53 template<__has_integral_minus _Tp>
54 requires (!__has_member_difference_type<_Tp>)
55 struct incrementable_traits<_Tp> {
56   using difference_type = make_signed_t<decltype(declval<_Tp>() - declval<_Tp>())>;
57 };
58 
59 template <class>
60 struct iterator_traits;
61 
62 // Let `RI` be `remove_cvref_t<I>`. The type `iter_difference_t<I>` denotes
63 // `incrementable_traits<RI>::difference_type` if `iterator_traits<RI>` names a specialization
64 // generated from the primary template, and `iterator_traits<RI>::difference_type` otherwise.
65 template <class _Ip>
66 using iter_difference_t = typename conditional_t<__is_primary_template<iterator_traits<remove_cvref_t<_Ip> > >::value,
67                                                  incrementable_traits<remove_cvref_t<_Ip> >,
68                                                  iterator_traits<remove_cvref_t<_Ip> > >::difference_type;
69 
70 #endif // _LIBCPP_STD_VER > 17
71 
72 _LIBCPP_END_NAMESPACE_STD
73 
74 #endif // _LIBCPP___ITERATOR_INCREMENTABLE_TRAITS_H
75