libcxx/include/__iterator/readable_traits.h

   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 >= 20
  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 #endif // _LIBCPP_STD_VER >= 20
  78
  79 _LIBCPP_END_NAMESPACE_STD
  80
  81 #endif // _LIBCPP___ITERATOR_READABLE_TRAITS_H