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