libstdc++
ptr_traits.h
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1 // Pointer Traits -*- C++ -*-
2 
3 // Copyright (C) 2011-2021 Free Software Foundation, Inc.
4 //
5 // This file is part of the GNU ISO C++ Library. This library is free
6 // software; you can redistribute it and/or modify it under the
7 // terms of the GNU General Public License as published by the
8 // Free Software Foundation; either version 3, or (at your option)
9 // any later version.
10 
11 // This library is distributed in the hope that it will be useful,
12 // but WITHOUT ANY WARRANTY; without even the implied warranty of
13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 // GNU General Public License for more details.
15 
16 // Under Section 7 of GPL version 3, you are granted additional
17 // permissions described in the GCC Runtime Library Exception, version
18 // 3.1, as published by the Free Software Foundation.
19 
20 // You should have received a copy of the GNU General Public License and
21 // a copy of the GCC Runtime Library Exception along with this program;
22 // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
23 // <http://www.gnu.org/licenses/>.
24 
25 /** @file bits/ptr_traits.h
26  * This is an internal header file, included by other library headers.
27  * Do not attempt to use it directly. @headername{memory}
28  */
29 
30 #ifndef _PTR_TRAITS_H
31 #define _PTR_TRAITS_H 1
32 
33 #if __cplusplus >= 201103L
34 
35 #include <bits/move.h>
36 
37 #if __cplusplus > 201703L
38 #define __cpp_lib_constexpr_memory 201811L
39 namespace __gnu_debug { struct _Safe_iterator_base; }
40 #endif
41 
42 namespace std _GLIBCXX_VISIBILITY(default)
43 {
44 _GLIBCXX_BEGIN_NAMESPACE_VERSION
45 
46  class __undefined;
47 
48  // Given Template<T, ...> and U return Template<U, ...>, otherwise invalid.
49  template<typename _Tp, typename _Up>
50  struct __replace_first_arg
51  { };
52 
53  template<template<typename, typename...> class _Template, typename _Up,
54  typename _Tp, typename... _Types>
55  struct __replace_first_arg<_Template<_Tp, _Types...>, _Up>
56  { using type = _Template<_Up, _Types...>; };
57 
58  template<typename _Tp, typename _Up>
59  using __replace_first_arg_t = typename __replace_first_arg<_Tp, _Up>::type;
60 
61  template<typename _Tp>
62  using __make_not_void
63  = typename conditional<is_void<_Tp>::value, __undefined, _Tp>::type;
64 
65  template<typename _Ptr>
66  struct __ptr_traits_elem_1
67  { };
68 
69  template<template<typename, typename...> class _SomePointer, typename _Tp,
70  typename... _Args>
71  struct __ptr_traits_elem_1<_SomePointer<_Tp, _Args...>>
72  {
73  using element_type = _Tp;
74  using pointer = _SomePointer<_Tp, _Args...>;
75 
76  static pointer
77  pointer_to(__make_not_void<element_type>& __e)
78  { return pointer::pointer_to(__e); }
79  };
80 
81  template<typename _Ptr, typename = void>
82  struct __ptr_traits_elem : __ptr_traits_elem_1<_Ptr>
83  { };
84 
85  template<typename _Ptr>
86  struct __ptr_traits_elem<_Ptr, __void_t<typename _Ptr::element_type>>
87  {
88  using element_type = typename _Ptr::element_type;
89 
90  static _Ptr
91  pointer_to(__make_not_void<element_type>& __e)
92  { return _Ptr::pointer_to(__e); }
93  };
94 
95  /**
96  * @brief Uniform interface to all pointer-like types
97  * @ingroup pointer_abstractions
98  */
99  template<typename _Ptr>
100  struct pointer_traits : __ptr_traits_elem<_Ptr>
101  {
102  private:
103  template<typename _Tp>
104  using __difference_type = typename _Tp::difference_type;
105 
106  template<typename _Tp, typename _Up, typename = void>
107  struct __rebind : __replace_first_arg<_Tp, _Up> { };
108 
109  template<typename _Tp, typename _Up>
110  struct __rebind<_Tp, _Up, __void_t<typename _Tp::template rebind<_Up>>>
111  { using type = typename _Tp::template rebind<_Up>; };
112 
113  public:
114  /// The pointer type.
115  using pointer = _Ptr;
116 
117  /// The type used to represent the difference between two pointers.
118  using difference_type
119  = __detected_or_t<ptrdiff_t, __difference_type, _Ptr>;
120 
121  /// A pointer to a different type.
122  template<typename _Up>
123  using rebind = typename __rebind<_Ptr, _Up>::type;
124  };
125 
126  /**
127  * @brief Partial specialization for built-in pointers.
128  * @ingroup pointer_abstractions
129  */
130  template<typename _Tp>
131  struct pointer_traits<_Tp*>
132  {
133  /// The pointer type
134  typedef _Tp* pointer;
135  /// The type pointed to
136  typedef _Tp element_type;
137  /// Type used to represent the difference between two pointers
138  typedef ptrdiff_t difference_type;
139 
140  template<typename _Up>
141  using rebind = _Up*;
142 
143  /**
144  * @brief Obtain a pointer to an object
145  * @param __r A reference to an object of type @c element_type
146  * @return @c addressof(__r)
147  */
148  static _GLIBCXX20_CONSTEXPR pointer
149  pointer_to(__make_not_void<element_type>& __r) noexcept
150  { return std::addressof(__r); }
151  };
152 
153  /// Convenience alias for rebinding pointers.
154  template<typename _Ptr, typename _Tp>
155  using __ptr_rebind = typename pointer_traits<_Ptr>::template rebind<_Tp>;
156 
157  template<typename _Tp>
158  constexpr _Tp*
159  __to_address(_Tp* __ptr) noexcept
160  {
161  static_assert(!std::is_function<_Tp>::value, "not a function pointer");
162  return __ptr;
163  }
164 
165 #if __cplusplus <= 201703L
166  template<typename _Ptr>
167  constexpr typename std::pointer_traits<_Ptr>::element_type*
168  __to_address(const _Ptr& __ptr)
169  { return std::__to_address(__ptr.operator->()); }
170 #else
171 
172  template<typename _Ptr>
173  constexpr auto
174  __to_address(const _Ptr& __ptr) noexcept
175  -> decltype(std::pointer_traits<_Ptr>::to_address(__ptr))
176  { return std::pointer_traits<_Ptr>::to_address(__ptr); }
177 
178  template<typename _Ptr, typename... _None>
179  constexpr auto
180  __to_address(const _Ptr& __ptr, _None...) noexcept
181  {
182  if constexpr (is_base_of_v<__gnu_debug::_Safe_iterator_base, _Ptr>)
183  return std::__to_address(__ptr.base().operator->());
184  else
185  return std::__to_address(__ptr.operator->());
186  }
187 
188 #define __cpp_lib_to_address 201711L
189 
190  /**
191  * @brief Obtain address referenced by a pointer to an object
192  * @param __ptr A pointer to an object
193  * @return @c __ptr
194  * @ingroup pointer_abstractions
195  */
196  template<typename _Tp>
197  constexpr _Tp*
198  to_address(_Tp* __ptr) noexcept
199  { return std::__to_address(__ptr); }
200 
201  /**
202  * @brief Obtain address referenced by a pointer to an object
203  * @param __ptr A pointer to an object
204  * @return @c pointer_traits<_Ptr>::to_address(__ptr) if that expression is
205  well-formed, otherwise @c to_address(__ptr.operator->())
206  * @ingroup pointer_abstractions
207  */
208  template<typename _Ptr>
209  constexpr auto
210  to_address(const _Ptr& __ptr) noexcept
211  { return std::__to_address(__ptr); }
212 #endif // C++2a
213 
214 _GLIBCXX_END_NAMESPACE_VERSION
215 } // namespace std
216 
217 #endif
218 
219 #endif
static constexpr pointer pointer_to(__make_not_void< element_type > &__r) noexcept
Obtain a pointer to an object.
Definition: ptr_traits.h:149
constexpr _Tp * addressof(_Tp &__r) noexcept
Returns the actual address of the object or function referenced by r, even in the presence of an over...
Definition: move.h:145
ptrdiff_t difference_type
Type used to represent the difference between two pointers.
Definition: ptr_traits.h:138
typename __rebind< _Ptr, _Up >::type rebind
A pointer to a different type.
Definition: ptr_traits.h:123
_Tp element_type
The type pointed to.
Definition: ptr_traits.h:136
GNU debug classes for public use.
typename pointer_traits< _Ptr >::template rebind< _Tp > __ptr_rebind
Convenience alias for rebinding pointers.
Definition: ptr_traits.h:155
Uniform interface to all pointer-like types.
Definition: ptr_traits.h:100
is_function
Definition: type_traits:212
_Ptr pointer
The pointer type.
Definition: ptr_traits.h:115
_Tp * pointer
The pointer type.
Definition: ptr_traits.h:134
__detected_or_t< ptrdiff_t, __difference_type, _Ptr > difference_type
The type used to represent the difference between two pointers.
Definition: ptr_traits.h:119
ISO C++ entities toplevel namespace is std.