libcxx/include/__iterator/incrementable_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_INCREMENTABLE_TRAITS_H
  11 #define _LIBCPP___ITERATOR_INCREMENTABLE_TRAITS_H
  12
  13 #include <__concepts/arithmetic.h>
  14 #include <__config>
  15 #include <__type_traits/conditional.h>
  16 #include <__type_traits/is_object.h>
  17 #include <__type_traits/is_primary_template.h>
  18 #include <__type_traits/make_signed.h>
  19 #include <__type_traits/remove_cvref.h>
  20 #include <__utility/declval.h>
  21 #include <cstddef>
  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 // [incrementable.traits]
  32 template<class> struct incrementable_traits {};
  33
  34 template<class _Tp>
  35 requires is_object_v<_Tp>
  36 struct incrementable_traits<_Tp*> {
  37   using difference_type = ptrdiff_t;
  38 };
  39
  40 template<class _Ip>
  41 struct incrementable_traits<const _Ip> : incrementable_traits<_Ip> {};
  42
  43 template<class _Tp>
  44 concept __has_member_difference_type = requires { typename _Tp::difference_type; };
  45
  46 template<__has_member_difference_type _Tp>
  47 struct incrementable_traits<_Tp> {
  48   using difference_type = typename _Tp::difference_type;
  49 };
  50
  51 template<class _Tp>
  52 concept __has_integral_minus =
  53   requires(const _Tp& __x, const _Tp& __y) {
  54     { __x - __y } -> integral;
  55   };
  56
  57 template<__has_integral_minus _Tp>
  58 requires (!__has_member_difference_type<_Tp>)
  59 struct incrementable_traits<_Tp> {
  60   using difference_type = make_signed_t<decltype(std::declval<_Tp>() - std::declval<_Tp>())>;
  61 };
  62
  63 template <class>
  64 struct iterator_traits;
  65
  66 // Let `RI` be `remove_cvref_t<I>`. The type `iter_difference_t<I>` denotes
  67 // `incrementable_traits<RI>::difference_type` if `iterator_traits<RI>` names a specialization
  68 // generated from the primary template, and `iterator_traits<RI>::difference_type` otherwise.
  69 template <class _Ip>
  70 using iter_difference_t = typename conditional_t<__is_primary_template<iterator_traits<remove_cvref_t<_Ip> > >::value,
  71                                                  incrementable_traits<remove_cvref_t<_Ip> >,
  72                                                  iterator_traits<remove_cvref_t<_Ip> > >::difference_type;
  73
  74 #endif // _LIBCPP_STD_VER >= 20
  75
  76 _LIBCPP_END_NAMESPACE_STD
  77
  78 #endif // _LIBCPP___ITERATOR_INCREMENTABLE_TRAITS_H