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 <__cstddef/ptrdiff_t.h>
  16 #include <__type_traits/conditional.h>
  17 #include <__type_traits/is_object.h>
  18 #include <__type_traits/is_primary_template.h>
  19 #include <__type_traits/make_signed.h>
  20 #include <__type_traits/remove_cvref.h>
  21 #include <__utility/declval.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 // [incrementable.traits]
  32 template <class>
  33 struct incrementable_traits {};
  34
  35 template <class _Tp>
  36   requires is_object_v<_Tp>
  37 struct incrementable_traits<_Tp*> {
  38   using difference_type = ptrdiff_t;
  39 };
  40
  41 template <class _Ip>
  42 struct incrementable_traits<const _Ip> : incrementable_traits<_Ip> {};
  43
  44 template <class _Tp>
  45 concept __has_member_difference_type = requires { typename _Tp::difference_type; };
  46
  47 template <__has_member_difference_type _Tp>
  48 struct incrementable_traits<_Tp> {
  49   using difference_type = typename _Tp::difference_type;
  50 };
  51
  52 template <class _Tp>
  53 concept __has_integral_minus = 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 =
  71     typename conditional_t<__is_primary_template<iterator_traits<remove_cvref_t<_Ip> > >::value,
  72                            incrementable_traits<remove_cvref_t<_Ip> >,
  73                            iterator_traits<remove_cvref_t<_Ip> > >::difference_type;
  74
  75 #endif // _LIBCPP_STD_VER >= 20
  76
  77 _LIBCPP_END_NAMESPACE_STD
  78
  79 #endif // _LIBCPP___ITERATOR_INCREMENTABLE_TRAITS_H