xref: /freebsd/contrib/llvm-project/libcxx/include/__iterator/incrementable_traits.h (revision 833a452e9f082a7982a31c21f0da437dbbe0a39d)
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_PUSH_MACROS
22 #include <__undef_macros>
23 
24 _LIBCPP_BEGIN_NAMESPACE_STD
25 
26 #if !defined(_LIBCPP_HAS_NO_RANGES)
27 
28 // [incrementable.traits]
29 template<class> struct incrementable_traits {};
30 
31 template<class _Tp>
32 requires is_object_v<_Tp>
33 struct incrementable_traits<_Tp*> {
34   using difference_type = ptrdiff_t;
35 };
36 
37 template<class _Ip>
38 struct incrementable_traits<const _Ip> : incrementable_traits<_Ip> {};
39 
40 template<class _Tp>
41 concept __has_member_difference_type = requires { typename _Tp::difference_type; };
42 
43 template<__has_member_difference_type _Tp>
44 struct incrementable_traits<_Tp> {
45   using difference_type = typename _Tp::difference_type;
46 };
47 
48 template<class _Tp>
49 concept __has_integral_minus =
50   requires(const _Tp& __x, const _Tp& __y) {
51     { __x - __y } -> integral;
52   };
53 
54 template<__has_integral_minus _Tp>
55 requires (!__has_member_difference_type<_Tp>)
56 struct incrementable_traits<_Tp> {
57   using difference_type = make_signed_t<decltype(declval<_Tp>() - declval<_Tp>())>;
58 };
59 
60 template <class>
61 struct iterator_traits;
62 
63 // Let `RI` be `remove_cvref_t<I>`. The type `iter_difference_t<I>` denotes
64 // `incrementable_traits<RI>::difference_type` if `iterator_traits<RI>` names a specialization
65 // generated from the primary template, and `iterator_traits<RI>::difference_type` otherwise.
66 template <class _Ip>
67 using iter_difference_t = typename conditional_t<__is_primary_template<iterator_traits<remove_cvref_t<_Ip> > >::value,
68                                                  incrementable_traits<remove_cvref_t<_Ip> >,
69                                                  iterator_traits<remove_cvref_t<_Ip> > >::difference_type;
70 
71 #endif // !defined(_LIBCPP_HAS_NO_RANGES)
72 
73 _LIBCPP_END_NAMESPACE_STD
74 
75 _LIBCPP_POP_MACROS
76 
77 #endif // _LIBCPP___ITERATOR_INCREMENTABLE_TRAITS_H
78