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, ...> return T, otherwise invalid.
49  template<typename _Tp>
50  struct __get_first_arg
51  { using type = __undefined; };
52 
53  template<template<typename, typename...> class _Template, typename _Tp,
54  typename... _Types>
55  struct __get_first_arg<_Template<_Tp, _Types...>>
56  { using type = _Tp; };
57 
58  template<typename _Tp>
59  using __get_first_arg_t = typename __get_first_arg<_Tp>::type;
60 
61  // Given Template<T, ...> and U return Template<U, ...>, otherwise invalid.
62  template<typename _Tp, typename _Up>
63  struct __replace_first_arg
64  { };
65 
66  template<template<typename, typename...> class _Template, typename _Up,
67  typename _Tp, typename... _Types>
68  struct __replace_first_arg<_Template<_Tp, _Types...>, _Up>
69  { using type = _Template<_Up, _Types...>; };
70 
71  template<typename _Tp, typename _Up>
72  using __replace_first_arg_t = typename __replace_first_arg<_Tp, _Up>::type;
73 
74  template<typename _Tp>
75  using __make_not_void
76  = typename conditional<is_void<_Tp>::value, __undefined, _Tp>::type;
77 
78  /**
79  * @brief Uniform interface to all pointer-like types
80  * @ingroup pointer_abstractions
81  */
82  template<typename _Ptr>
84  {
85  private:
86  template<typename _Tp>
87  using __element_type = typename _Tp::element_type;
88 
89  template<typename _Tp>
90  using __difference_type = typename _Tp::difference_type;
91 
92  template<typename _Tp, typename _Up, typename = void>
93  struct __rebind : __replace_first_arg<_Tp, _Up> { };
94 
95  template<typename _Tp, typename _Up>
96  struct __rebind<_Tp, _Up, __void_t<typename _Tp::template rebind<_Up>>>
97  { using type = typename _Tp::template rebind<_Up>; };
98 
99  public:
100  /// The pointer type.
101  using pointer = _Ptr;
102 
103  /// The type pointed to.
105  = __detected_or_t<__get_first_arg_t<_Ptr>, __element_type, _Ptr>;
106 
107  /// The type used to represent the difference between two pointers.
109  = __detected_or_t<ptrdiff_t, __difference_type, _Ptr>;
110 
111  /// A pointer to a different type.
112  template<typename _Up>
113  using rebind = typename __rebind<_Ptr, _Up>::type;
114 
115  static _Ptr
116  pointer_to(__make_not_void<element_type>& __e)
117  { return _Ptr::pointer_to(__e); }
118 
120  "pointer type defines element_type or is like SomePointer<T, Args>");
121  };
122 
123  /**
124  * @brief Partial specialization for built-in pointers.
125  * @ingroup pointer_abstractions
126  */
127  template<typename _Tp>
128  struct pointer_traits<_Tp*>
129  {
130  /// The pointer type
131  typedef _Tp* pointer;
132  /// The type pointed to
133  typedef _Tp element_type;
134  /// Type used to represent the difference between two pointers
135  typedef ptrdiff_t difference_type;
136 
137  template<typename _Up>
138  using rebind = _Up*;
139 
140  /**
141  * @brief Obtain a pointer to an object
142  * @param __r A reference to an object of type @c element_type
143  * @return @c addressof(__r)
144  */
145  static _GLIBCXX20_CONSTEXPR pointer
146  pointer_to(__make_not_void<element_type>& __r) noexcept
147  { return std::addressof(__r); }
148  };
149 
150  /// Convenience alias for rebinding pointers.
151  template<typename _Ptr, typename _Tp>
152  using __ptr_rebind = typename pointer_traits<_Ptr>::template rebind<_Tp>;
153 
154  template<typename _Tp>
155  constexpr _Tp*
156  __to_address(_Tp* __ptr) noexcept
157  {
158  static_assert(!std::is_function<_Tp>::value, "not a function pointer");
159  return __ptr;
160  }
161 
162 #if __cplusplus <= 201703L
163  template<typename _Ptr>
164  constexpr typename std::pointer_traits<_Ptr>::element_type*
165  __to_address(const _Ptr& __ptr)
166  { return std::__to_address(__ptr.operator->()); }
167 #else
168  template<typename _Ptr>
169  constexpr auto
170  __to_address(const _Ptr& __ptr) noexcept
171  -> decltype(std::pointer_traits<_Ptr>::to_address(__ptr))
172  { return std::pointer_traits<_Ptr>::to_address(__ptr); }
173 
174  template<typename _Ptr, typename... _None>
175  constexpr auto
176  __to_address(const _Ptr& __ptr, _None...) noexcept
177  {
178  if constexpr (is_base_of_v<__gnu_debug::_Safe_iterator_base, _Ptr>)
179  return std::__to_address(__ptr.base().operator->());
180  else
181  return std::__to_address(__ptr.operator->());
182  }
183 
184 #define __cpp_lib_to_address 201711L
185 
186  /**
187  * @brief Obtain address referenced by a pointer to an object
188  * @param __ptr A pointer to an object
189  * @return @c __ptr
190  * @ingroup pointer_abstractions
191  */
192  template<typename _Tp>
193  constexpr _Tp*
194  to_address(_Tp* __ptr) noexcept
195  { return std::__to_address(__ptr); }
196 
197  /**
198  * @brief Obtain address referenced by a pointer to an object
199  * @param __ptr A pointer to an object
200  * @return @c pointer_traits<_Ptr>::to_address(__ptr) if that expression is
201  well-formed, otherwise @c to_address(__ptr.operator->())
202  * @ingroup pointer_abstractions
203  */
204  template<typename _Ptr>
205  constexpr auto
206  to_address(const _Ptr& __ptr) noexcept
207  { return std::__to_address(__ptr); }
208 #endif // C++2a
209 
210 _GLIBCXX_END_NAMESPACE_VERSION
211 } // namespace std
212 
213 #endif
214 
215 #endif
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
ISO C++ entities toplevel namespace is std.
typename pointer_traits< _Ptr >::template rebind< _Tp > __ptr_rebind
Convenience alias for rebinding pointers.
Definition: ptr_traits.h:152
GNU debug classes for public use.
is_function
Definition: type_traits:520
is_same
Definition: type_traits:1410
Uniform interface to all pointer-like types.
Definition: ptr_traits.h:84
__detected_or_t< __get_first_arg_t< _Ptr >, __element_type, _Ptr > element_type
The type pointed to.
Definition: ptr_traits.h:105
typename __rebind< _Ptr, _Up >::type rebind
A pointer to a different type.
Definition: ptr_traits.h:113
_Ptr pointer
The pointer type.
Definition: ptr_traits.h:101
__detected_or_t< ptrdiff_t, __difference_type, _Ptr > difference_type
The type used to represent the difference between two pointers.
Definition: ptr_traits.h:109
_Tp * pointer
The pointer type.
Definition: ptr_traits.h:131
ptrdiff_t difference_type
Type used to represent the difference between two pointers.
Definition: ptr_traits.h:135
_Tp element_type
The type pointed to.
Definition: ptr_traits.h:133
static constexpr pointer pointer_to(__make_not_void< element_type > &__r) noexcept
Obtain a pointer to an object.
Definition: ptr_traits.h:146