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_PUSH_MACROS
22 #include <__undef_macros>
23 
24 _LIBCPP_BEGIN_NAMESPACE_STD
25 
26 #if !defined(_LIBCPP_HAS_NO_RANGES)
27 
28 // [readable.traits]
29 template<class> struct __cond_value_type {};
30 
31 template<class _Tp>
32 requires is_object_v<_Tp>
33 struct __cond_value_type<_Tp> { using value_type = remove_cv_t<_Tp>; };
34 
35 template<class _Tp>
36 concept __has_member_value_type = requires { typename _Tp::value_type; };
37 
38 template<class _Tp>
39 concept __has_member_element_type = requires { typename _Tp::element_type; };
40 
41 template<class> struct indirectly_readable_traits {};
42 
43 template<class _Ip>
44 requires is_array_v<_Ip>
45 struct indirectly_readable_traits<_Ip> {
46   using value_type = remove_cv_t<remove_extent_t<_Ip>>;
47 };
48 
49 template<class _Ip>
50 struct indirectly_readable_traits<const _Ip> : indirectly_readable_traits<_Ip> {};
51 
52 template<class _Tp>
53 struct indirectly_readable_traits<_Tp*> : __cond_value_type<_Tp> {};
54 
55 template<__has_member_value_type _Tp>
56 struct indirectly_readable_traits<_Tp>
57   : __cond_value_type<typename _Tp::value_type> {};
58 
59 template<__has_member_element_type _Tp>
60 struct indirectly_readable_traits<_Tp>
61   : __cond_value_type<typename _Tp::element_type> {};
62 
63 // Pre-emptively applies LWG3541
64 template<__has_member_value_type _Tp>
65 requires __has_member_element_type<_Tp>
66 struct indirectly_readable_traits<_Tp> {};
67 template<__has_member_value_type _Tp>
68 requires __has_member_element_type<_Tp> &&
69          same_as<remove_cv_t<typename _Tp::element_type>,
70                  remove_cv_t<typename _Tp::value_type>>
71 struct indirectly_readable_traits<_Tp>
72   : __cond_value_type<typename _Tp::value_type> {};
73 
74 template <class>
75 struct iterator_traits;
76 
77 // Let `RI` be `remove_cvref_t<I>`. The type `iter_value_t<I>` denotes
78 // `indirectly_readable_traits<RI>::value_type` if `iterator_traits<RI>` names a specialization
79 // generated from the primary template, and `iterator_traits<RI>::value_type` otherwise.
80 template <class _Ip>
81 using iter_value_t = typename conditional_t<__is_primary_template<iterator_traits<remove_cvref_t<_Ip> > >::value,
82                                             indirectly_readable_traits<remove_cvref_t<_Ip> >,
83                                             iterator_traits<remove_cvref_t<_Ip> > >::value_type;
84 
85 #endif // !defined(_LIBCPP_HAS_NO_RANGES)
86 
87 _LIBCPP_END_NAMESPACE_STD
88 
89 _LIBCPP_POP_MACROS
90 
91 #endif // _LIBCPP___ITERATOR_READABLE_TRAITS_H
92