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 <__iterator/concepts.h>
15 
16 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
17 #pragma GCC system_header
18 #endif
19 
20 _LIBCPP_PUSH_MACROS
21 #include <__undef_macros>
22 
23 _LIBCPP_BEGIN_NAMESPACE_STD
24 
25 #if !defined(_LIBCPP_HAS_NO_RANGES)
26 
27 // [readable.traits]
28 template<class> struct __cond_value_type {};
29 
30 template<class _Tp>
31 requires is_object_v<_Tp>
32 struct __cond_value_type<_Tp> { using value_type = remove_cv_t<_Tp>; };
33 
34 template<class _Tp>
35 concept __has_member_value_type = requires { typename _Tp::value_type; };
36 
37 template<class _Tp>
38 concept __has_member_element_type = requires { typename _Tp::element_type; };
39 
40 template<class> struct indirectly_readable_traits {};
41 
42 template<class _Ip>
43 requires is_array_v<_Ip>
44 struct indirectly_readable_traits<_Ip> {
45   using value_type = remove_cv_t<remove_extent_t<_Ip>>;
46 };
47 
48 template<class _Ip>
49 struct indirectly_readable_traits<const _Ip> : indirectly_readable_traits<_Ip> {};
50 
51 template<class _Tp>
52 struct indirectly_readable_traits<_Tp*> : __cond_value_type<_Tp> {};
53 
54 template<__has_member_value_type _Tp>
55 struct indirectly_readable_traits<_Tp>
56   : __cond_value_type<typename _Tp::value_type> {};
57 
58 template<__has_member_element_type _Tp>
59 struct indirectly_readable_traits<_Tp>
60   : __cond_value_type<typename _Tp::element_type> {};
61 
62 // Pre-emptively applies LWG3541
63 template<__has_member_value_type _Tp>
64 requires __has_member_element_type<_Tp>
65 struct indirectly_readable_traits<_Tp> {};
66 template<__has_member_value_type _Tp>
67 requires __has_member_element_type<_Tp> &&
68          same_as<remove_cv_t<typename _Tp::element_type>,
69                  remove_cv_t<typename _Tp::value_type>>
70 struct indirectly_readable_traits<_Tp>
71   : __cond_value_type<typename _Tp::value_type> {};
72 
73 template <class>
74 struct iterator_traits;
75 
76 // Let `RI` be `remove_­cvref_­t<I>`. The type `iter_­value_­t<I>` denotes
77 // `indirectly_­readable_­traits<RI>::value_­type` if `iterator_­traits<RI>` names a specialization
78 // generated from the primary template, and `iterator_­traits<RI>::value_­type` otherwise.
79 template <class _Ip>
80 using iter_value_t = typename conditional_t<__is_primary_template<iterator_traits<remove_cvref_t<_Ip> > >::value,
81                                             indirectly_readable_traits<remove_cvref_t<_Ip> >,
82                                             iterator_traits<remove_cvref_t<_Ip> > >::value_type;
83 
84 #endif // !defined(_LIBCPP_HAS_NO_RANGES)
85 
86 _LIBCPP_END_NAMESPACE_STD
87 
88 _LIBCPP_POP_MACROS
89 
90 #endif // _LIBCPP___ITERATOR_READABLE_TRAITS_H
91