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 <__concepts/same_as.h> 14 #include <__config> 15 #include <__type_traits/conditional.h> 16 #include <__type_traits/is_array.h> 17 #include <__type_traits/is_object.h> 18 #include <__type_traits/is_primary_template.h> 19 #include <__type_traits/remove_cv.h> 20 #include <__type_traits/remove_cvref.h> 21 #include <__type_traits/remove_extent.h> 22 23 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) 24 # pragma GCC system_header 25 #endif 26 27 _LIBCPP_BEGIN_NAMESPACE_STD 28 29 #if _LIBCPP_STD_VER > 17 30 31 // [readable.traits] 32 template<class> struct __cond_value_type {}; 33 34 template<class _Tp> 35 requires is_object_v<_Tp> 36 struct __cond_value_type<_Tp> { using value_type = remove_cv_t<_Tp>; }; 37 38 template<class _Tp> 39 concept __has_member_value_type = requires { typename _Tp::value_type; }; 40 41 template<class _Tp> 42 concept __has_member_element_type = requires { typename _Tp::element_type; }; 43 44 template<class> struct indirectly_readable_traits {}; 45 46 template<class _Ip> 47 requires is_array_v<_Ip> 48 struct indirectly_readable_traits<_Ip> { 49 using value_type = remove_cv_t<remove_extent_t<_Ip>>; 50 }; 51 52 template<class _Ip> 53 struct indirectly_readable_traits<const _Ip> : indirectly_readable_traits<_Ip> {}; 54 55 template<class _Tp> 56 struct indirectly_readable_traits<_Tp*> : __cond_value_type<_Tp> {}; 57 58 template<__has_member_value_type _Tp> 59 struct indirectly_readable_traits<_Tp> 60 : __cond_value_type<typename _Tp::value_type> {}; 61 62 template<__has_member_element_type _Tp> 63 struct indirectly_readable_traits<_Tp> 64 : __cond_value_type<typename _Tp::element_type> {}; 65 66 template<__has_member_value_type _Tp> 67 requires __has_member_element_type<_Tp> 68 struct indirectly_readable_traits<_Tp> {}; 69 70 template<__has_member_value_type _Tp> 71 requires __has_member_element_type<_Tp> && 72 same_as<remove_cv_t<typename _Tp::element_type>, 73 remove_cv_t<typename _Tp::value_type>> 74 struct indirectly_readable_traits<_Tp> 75 : __cond_value_type<typename _Tp::value_type> {}; 76 77 template <class> 78 struct iterator_traits; 79 80 // Let `RI` be `remove_cvref_t<I>`. The type `iter_value_t<I>` denotes 81 // `indirectly_readable_traits<RI>::value_type` if `iterator_traits<RI>` names a specialization 82 // generated from the primary template, and `iterator_traits<RI>::value_type` otherwise. 83 template <class _Ip> 84 using iter_value_t = typename conditional_t<__is_primary_template<iterator_traits<remove_cvref_t<_Ip> > >::value, 85 indirectly_readable_traits<remove_cvref_t<_Ip> >, 86 iterator_traits<remove_cvref_t<_Ip> > >::value_type; 87 88 #endif // _LIBCPP_STD_VER > 17 89 90 _LIBCPP_END_NAMESPACE_STD 91 92 #endif // _LIBCPP___ITERATOR_READABLE_TRAITS_H 93