libstdc++
ptr_traits.h
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1 // Pointer Traits -*- C++ -*-
2 
3 // Copyright (C) 2011-2024 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 #include <concepts>
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  /// @cond undocumented
47 
48  class __undefined;
49 
50  // For a specialization `SomeTemplate<T, Types...>` the member `type` is T,
51  // otherwise `type` is `__undefined`.
52  template<typename _Tp>
53  struct __get_first_arg
54  { using type = __undefined; };
55 
56  template<template<typename, typename...> class _SomeTemplate, typename _Tp,
57  typename... _Types>
58  struct __get_first_arg<_SomeTemplate<_Tp, _Types...>>
59  { using type = _Tp; };
60 
61  // For a specialization `SomeTemplate<T, Args...>` and a type `U` the member
62  // `type` is `SomeTemplate<U, Args...>`, otherwise there is no member `type`.
63  template<typename _Tp, typename _Up>
64  struct __replace_first_arg
65  { };
66 
67  template<template<typename, typename...> class _SomeTemplate, typename _Up,
68  typename _Tp, typename... _Types>
69  struct __replace_first_arg<_SomeTemplate<_Tp, _Types...>, _Up>
70  { using type = _SomeTemplate<_Up, _Types...>; };
71 
72  // Detect the element type of a pointer-like type.
73  template<typename _Ptr, typename = void>
74  struct __ptr_traits_elem : __get_first_arg<_Ptr>
75  { };
76 
77  // Use _Ptr::element_type if is a valid type.
78 #if __cpp_concepts
79  template<typename _Ptr> requires requires { typename _Ptr::element_type; }
80  struct __ptr_traits_elem<_Ptr, void>
81  { using type = typename _Ptr::element_type; };
82 #else
83  template<typename _Ptr>
84  struct __ptr_traits_elem<_Ptr, __void_t<typename _Ptr::element_type>>
85  { using type = typename _Ptr::element_type; };
86 #endif
87 
88  template<typename _Ptr>
89  using __ptr_traits_elem_t = typename __ptr_traits_elem<_Ptr>::type;
90 
91  /// @endcond
92 
93  // Define pointer_traits<P>::pointer_to.
94  template<typename _Ptr, typename _Elt, bool = is_void<_Elt>::value>
95  struct __ptr_traits_ptr_to
96  {
97  using pointer = _Ptr;
98  using element_type = _Elt;
99 
100  /**
101  * @brief Obtain a pointer to an object
102  * @param __r A reference to an object of type `element_type`
103  * @return `pointer::pointer_to(__r)`
104  * @pre `pointer::pointer_to(__r)` is a valid expression.
105  */
106  static pointer
107  pointer_to(element_type& __r)
108 #if __cpp_lib_concepts
109  requires requires {
110  { pointer::pointer_to(__r) } -> convertible_to<pointer>;
111  }
112 #endif
113  { return pointer::pointer_to(__r); }
114  };
115 
116  // Do not define pointer_traits<P>::pointer_to if element type is void.
117  template<typename _Ptr, typename _Elt>
118  struct __ptr_traits_ptr_to<_Ptr, _Elt, true>
119  { };
120 
121  // Partial specialization defining pointer_traits<T*>::pointer_to(T&).
122  template<typename _Tp>
123  struct __ptr_traits_ptr_to<_Tp*, _Tp, false>
124  {
125  using pointer = _Tp*;
126  using element_type = _Tp;
127 
128  /**
129  * @brief Obtain a pointer to an object
130  * @param __r A reference to an object of type `element_type`
131  * @return `addressof(__r)`
132  */
133  static _GLIBCXX20_CONSTEXPR pointer
134  pointer_to(element_type& __r) noexcept
135  { return std::addressof(__r); }
136  };
137 
138  template<typename _Ptr, typename _Elt>
139  struct __ptr_traits_impl : __ptr_traits_ptr_to<_Ptr, _Elt>
140  {
141  private:
142  template<typename _Tp>
143  using __diff_t = typename _Tp::difference_type;
144 
145  template<typename _Tp, typename _Up>
146  using __rebind = __type_identity<typename _Tp::template rebind<_Up>>;
147 
148  public:
149  /// The pointer type.
150  using pointer = _Ptr;
151 
152  /// The type pointed to.
153  using element_type = _Elt;
154 
155  /// The type used to represent the difference between two pointers.
156  using difference_type = __detected_or_t<ptrdiff_t, __diff_t, _Ptr>;
157 
158  /// A pointer to a different type.
159  template<typename _Up>
160  using rebind = typename __detected_or_t<__replace_first_arg<_Ptr, _Up>,
161  __rebind, _Ptr, _Up>::type;
162  };
163 
164  // _GLIBCXX_RESOLVE_LIB_DEFECTS
165  // 3545. std::pointer_traits should be SFINAE-friendly
166  template<typename _Ptr>
167  struct __ptr_traits_impl<_Ptr, __undefined>
168  { };
169 
170  /**
171  * @brief Uniform interface to all pointer-like types
172  * @headerfile memory
173  * @ingroup pointer_abstractions
174  * @since C++11
175  */
176  template<typename _Ptr>
177  struct pointer_traits : __ptr_traits_impl<_Ptr, __ptr_traits_elem_t<_Ptr>>
178  { };
179 
180  /**
181  * @brief Partial specialization for built-in pointers.
182  * @headerfile memory
183  * @ingroup pointer_abstractions
184  * @since C++11
185  */
186  template<typename _Tp>
187  struct pointer_traits<_Tp*> : __ptr_traits_ptr_to<_Tp*, _Tp>
188  {
189  /// The pointer type
190  typedef _Tp* pointer;
191  /// The type pointed to
192  typedef _Tp element_type;
193  /// Type used to represent the difference between two pointers
194  typedef ptrdiff_t difference_type;
195  /// A pointer to a different type.
196  template<typename _Up> using rebind = _Up*;
197  };
198 
199  /// Convenience alias for rebinding pointers.
200  template<typename _Ptr, typename _Tp>
201  using __ptr_rebind = typename pointer_traits<_Ptr>::template rebind<_Tp>;
202 
203  template<typename _Tp>
204  constexpr _Tp*
205  __to_address(_Tp* __ptr) noexcept
206  {
207  static_assert(!std::is_function<_Tp>::value, "not a function pointer");
208  return __ptr;
209  }
210 
211 #ifndef __glibcxx_to_address // C++ < 20
212  template<typename _Ptr>
213  constexpr typename std::pointer_traits<_Ptr>::element_type*
214  __to_address(const _Ptr& __ptr)
215  { return std::__to_address(__ptr.operator->()); }
216 #else
217  template<typename _Ptr>
218  constexpr auto
219  __to_address(const _Ptr& __ptr) noexcept
220  -> decltype(std::pointer_traits<_Ptr>::to_address(__ptr))
221  { return std::pointer_traits<_Ptr>::to_address(__ptr); }
222 
223  template<typename _Ptr, typename... _None>
224  constexpr auto
225  __to_address(const _Ptr& __ptr, _None...) noexcept
226  {
227  if constexpr (is_base_of_v<__gnu_debug::_Safe_iterator_base, _Ptr>)
228  return std::__to_address(__ptr.base().operator->());
229  else
230  return std::__to_address(__ptr.operator->());
231  }
232 
233  /**
234  * @brief Obtain address referenced by a pointer to an object
235  * @param __ptr A pointer to an object
236  * @return @c __ptr
237  * @ingroup pointer_abstractions
238  */
239  template<typename _Tp>
240  constexpr _Tp*
241  to_address(_Tp* __ptr) noexcept
242  { return std::__to_address(__ptr); }
243 
244  /**
245  * @brief Obtain address referenced by a pointer to an object
246  * @param __ptr A pointer to an object
247  * @return @c pointer_traits<_Ptr>::to_address(__ptr) if that expression is
248  well-formed, otherwise @c to_address(__ptr.operator->())
249  * @ingroup pointer_abstractions
250  */
251  template<typename _Ptr>
252  constexpr auto
253  to_address(const _Ptr& __ptr) noexcept
254  { return std::__to_address(__ptr); }
255 #endif // __glibcxx_to_address
256 
257 _GLIBCXX_END_NAMESPACE_VERSION
258 } // namespace std
259 
260 #endif
261 
262 #endif
ISO C++ entities toplevel namespace is std.
constexpr _Tp * to_address(_Tp *__ptr) noexcept
Obtain address referenced by a pointer to an object.
Definition: ptr_traits.h:241
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:162
_Tp element_type
The type pointed to.
Definition: ptr_traits.h:192
_Up * rebind
A pointer to a different type.
Definition: ptr_traits.h:196
ptrdiff_t difference_type
Type used to represent the difference between two pointers.
Definition: ptr_traits.h:194
Uniform interface to all pointer-like types.
Definition: ptr_traits.h:177
is_function
Definition: type_traits:280
GNU debug classes for public use.
constexpr auto to_address(const _Ptr &__ptr) noexcept
Obtain address referenced by a pointer to an object.
Definition: ptr_traits.h:253
_Tp * pointer
The pointer type.
Definition: ptr_traits.h:190
typename pointer_traits< _Ptr >::template rebind< _Tp > __ptr_rebind
Convenience alias for rebinding pointers.
Definition: ptr_traits.h:201