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_READABLE_TRAITS_H
11 #define _LIBCPP___ITERATOR_READABLE_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 // [readable.traits]
26 template<class> struct __cond_value_type {};
27 
28 template<class _Tp>
29 requires is_object_v<_Tp>
30 struct __cond_value_type<_Tp> { using value_type = remove_cv_t<_Tp>; };
31 
32 template<class _Tp>
33 concept __has_member_value_type = requires { typename _Tp::value_type; };
34 
35 template<class _Tp>
36 concept __has_member_element_type = requires { typename _Tp::element_type; };
37 
38 template<class> struct indirectly_readable_traits {};
39 
40 template<class _Ip>
41 requires is_array_v<_Ip>
42 struct indirectly_readable_traits<_Ip> {
43   using value_type = remove_cv_t<remove_extent_t<_Ip>>;
44 };
45 
46 template<class _Ip>
47 struct indirectly_readable_traits<const _Ip> : indirectly_readable_traits<_Ip> {};
48 
49 template<class _Tp>
50 struct indirectly_readable_traits<_Tp*> : __cond_value_type<_Tp> {};
51 
52 template<__has_member_value_type _Tp>
53 struct indirectly_readable_traits<_Tp>
54   : __cond_value_type<typename _Tp::value_type> {};
55 
56 template<__has_member_element_type _Tp>
57 struct indirectly_readable_traits<_Tp>
58   : __cond_value_type<typename _Tp::element_type> {};
59 
60 template<__has_member_value_type _Tp>
61   requires __has_member_element_type<_Tp>
62 struct indirectly_readable_traits<_Tp> {};
63 
64 template<__has_member_value_type _Tp>
65   requires __has_member_element_type<_Tp> &&
66            same_as<remove_cv_t<typename _Tp::element_type>,
67                    remove_cv_t<typename _Tp::value_type>>
68 struct indirectly_readable_traits<_Tp>
69   : __cond_value_type<typename _Tp::value_type> {};
70 
71 template <class>
72 struct iterator_traits;
73 
74 // Let `RI` be `remove_cvref_t<I>`. The type `iter_value_t<I>` denotes
75 // `indirectly_readable_traits<RI>::value_type` if `iterator_traits<RI>` names a specialization
76 // generated from the primary template, and `iterator_traits<RI>::value_type` otherwise.
77 template <class _Ip>
78 using iter_value_t = typename conditional_t<__is_primary_template<iterator_traits<remove_cvref_t<_Ip> > >::value,
79                                             indirectly_readable_traits<remove_cvref_t<_Ip> >,
80                                             iterator_traits<remove_cvref_t<_Ip> > >::value_type;
81 
82 #endif // _LIBCPP_STD_VER > 17
83 
84 _LIBCPP_END_NAMESPACE_STD
85 
86 #endif // _LIBCPP___ITERATOR_READABLE_TRAITS_H
87