libstdc++
ptr_traits.h
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1 // Pointer Traits -*- C++ -*-
2 
3 // Copyright (C) 2011-2023 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 /* Duplicate definition with unique_ptr.h. */
38 #if __cplusplus > 202002L && defined(__cpp_constexpr_dynamic_alloc)
39 # define __cpp_lib_constexpr_memory 202202L
40 #elif __cplusplus > 201703L
41 # define __cpp_lib_constexpr_memory 201811L
42 #endif
43 
44 #if __cplusplus > 201703L
45 #include <concepts>
46 namespace __gnu_debug { struct _Safe_iterator_base; }
47 #endif
48 
49 namespace std _GLIBCXX_VISIBILITY(default)
50 {
51 _GLIBCXX_BEGIN_NAMESPACE_VERSION
52 
53  /// @cond undocumented
54 
55  class __undefined;
56 
57  // For a specialization `SomeTemplate<T, Types...>` the member `type` is T,
58  // otherwise `type` is `__undefined`.
59  template<typename _Tp>
60  struct __get_first_arg
61  { using type = __undefined; };
62 
63  template<template<typename, typename...> class _SomeTemplate, typename _Tp,
64  typename... _Types>
65  struct __get_first_arg<_SomeTemplate<_Tp, _Types...>>
66  { using type = _Tp; };
67 
68  // For a specialization `SomeTemplate<T, Args...>` and a type `U` the member
69  // `type` is `SomeTemplate<U, Args...>`, otherwise there is no member `type`.
70  template<typename _Tp, typename _Up>
71  struct __replace_first_arg
72  { };
73 
74  template<template<typename, typename...> class _SomeTemplate, typename _Up,
75  typename _Tp, typename... _Types>
76  struct __replace_first_arg<_SomeTemplate<_Tp, _Types...>, _Up>
77  { using type = _SomeTemplate<_Up, _Types...>; };
78 
79  // Detect the element type of a pointer-like type.
80  template<typename _Ptr, typename = void>
81  struct __ptr_traits_elem : __get_first_arg<_Ptr>
82  { };
83 
84  // Use _Ptr::element_type if is a valid type.
85 #if __cpp_concepts
86  template<typename _Ptr> requires requires { typename _Ptr::element_type; }
87  struct __ptr_traits_elem<_Ptr, void>
88  { using type = typename _Ptr::element_type; };
89 #else
90  template<typename _Ptr>
91  struct __ptr_traits_elem<_Ptr, __void_t<typename _Ptr::element_type>>
92  { using type = typename _Ptr::element_type; };
93 #endif
94 
95  template<typename _Ptr>
96  using __ptr_traits_elem_t = typename __ptr_traits_elem<_Ptr>::type;
97 
98  /// @endcond
99 
100  // Define pointer_traits<P>::pointer_to.
101  template<typename _Ptr, typename _Elt, bool = is_void<_Elt>::value>
102  struct __ptr_traits_ptr_to
103  {
104  using pointer = _Ptr;
105  using element_type = _Elt;
106 
107  /**
108  * @brief Obtain a pointer to an object
109  * @param __r A reference to an object of type `element_type`
110  * @return `pointer::pointer_to(__r)`
111  * @pre `pointer::pointer_to(__r)` is a valid expression.
112  */
113  static pointer
114  pointer_to(element_type& __r)
115 #if __cpp_lib_concepts
116  requires requires {
117  { pointer::pointer_to(__r) } -> convertible_to<pointer>;
118  }
119 #endif
120  { return pointer::pointer_to(__r); }
121  };
122 
123  // Do not define pointer_traits<P>::pointer_to if element type is void.
124  template<typename _Ptr, typename _Elt>
125  struct __ptr_traits_ptr_to<_Ptr, _Elt, true>
126  { };
127 
128  // Partial specialization defining pointer_traits<T*>::pointer_to(T&).
129  template<typename _Tp>
130  struct __ptr_traits_ptr_to<_Tp*, _Tp, false>
131  {
132  using pointer = _Tp*;
133  using element_type = _Tp;
134 
135  /**
136  * @brief Obtain a pointer to an object
137  * @param __r A reference to an object of type `element_type`
138  * @return `addressof(__r)`
139  */
140  static _GLIBCXX20_CONSTEXPR pointer
141  pointer_to(element_type& __r) noexcept
142  { return std::addressof(__r); }
143  };
144 
145  template<typename _Ptr, typename _Elt>
146  struct __ptr_traits_impl : __ptr_traits_ptr_to<_Ptr, _Elt>
147  {
148  private:
149  template<typename _Tp>
150  using __diff_t = typename _Tp::difference_type;
151 
152  template<typename _Tp, typename _Up>
153  using __rebind = __type_identity<typename _Tp::template rebind<_Up>>;
154 
155  public:
156  /// The pointer type.
157  using pointer = _Ptr;
158 
159  /// The type pointed to.
160  using element_type = _Elt;
161 
162  /// The type used to represent the difference between two pointers.
163  using difference_type = __detected_or_t<ptrdiff_t, __diff_t, _Ptr>;
164 
165  /// A pointer to a different type.
166  template<typename _Up>
167  using rebind = typename __detected_or_t<__replace_first_arg<_Ptr, _Up>,
168  __rebind, _Ptr, _Up>::type;
169  };
170 
171  // _GLIBCXX_RESOLVE_LIB_DEFECTS
172  // 3545. std::pointer_traits should be SFINAE-friendly
173  template<typename _Ptr>
174  struct __ptr_traits_impl<_Ptr, __undefined>
175  { };
176 
177  /**
178  * @brief Uniform interface to all pointer-like types
179  * @headerfile memory
180  * @ingroup pointer_abstractions
181  * @since C++11
182  */
183  template<typename _Ptr>
184  struct pointer_traits : __ptr_traits_impl<_Ptr, __ptr_traits_elem_t<_Ptr>>
185  { };
186 
187  /**
188  * @brief Partial specialization for built-in pointers.
189  * @headerfile memory
190  * @ingroup pointer_abstractions
191  * @since C++11
192  */
193  template<typename _Tp>
194  struct pointer_traits<_Tp*> : __ptr_traits_ptr_to<_Tp*, _Tp>
195  {
196  /// The pointer type
197  typedef _Tp* pointer;
198  /// The type pointed to
199  typedef _Tp element_type;
200  /// Type used to represent the difference between two pointers
201  typedef ptrdiff_t difference_type;
202  /// A pointer to a different type.
203  template<typename _Up> using rebind = _Up*;
204  };
205 
206  /// Convenience alias for rebinding pointers.
207  template<typename _Ptr, typename _Tp>
208  using __ptr_rebind = typename pointer_traits<_Ptr>::template rebind<_Tp>;
209 
210  template<typename _Tp>
211  constexpr _Tp*
212  __to_address(_Tp* __ptr) noexcept
213  {
214  static_assert(!std::is_function<_Tp>::value, "not a function pointer");
215  return __ptr;
216  }
217 
218 #if __cplusplus <= 201703L
219  template<typename _Ptr>
220  constexpr typename std::pointer_traits<_Ptr>::element_type*
221  __to_address(const _Ptr& __ptr)
222  { return std::__to_address(__ptr.operator->()); }
223 #else
224  template<typename _Ptr>
225  constexpr auto
226  __to_address(const _Ptr& __ptr) noexcept
227  -> decltype(std::pointer_traits<_Ptr>::to_address(__ptr))
228  { return std::pointer_traits<_Ptr>::to_address(__ptr); }
229 
230  template<typename _Ptr, typename... _None>
231  constexpr auto
232  __to_address(const _Ptr& __ptr, _None...) noexcept
233  {
234  if constexpr (is_base_of_v<__gnu_debug::_Safe_iterator_base, _Ptr>)
235  return std::__to_address(__ptr.base().operator->());
236  else
237  return std::__to_address(__ptr.operator->());
238  }
239 
240 #define __cpp_lib_to_address 201711L
241 
242  /**
243  * @brief Obtain address referenced by a pointer to an object
244  * @param __ptr A pointer to an object
245  * @return @c __ptr
246  * @ingroup pointer_abstractions
247  */
248  template<typename _Tp>
249  constexpr _Tp*
250  to_address(_Tp* __ptr) noexcept
251  { return std::__to_address(__ptr); }
252 
253  /**
254  * @brief Obtain address referenced by a pointer to an object
255  * @param __ptr A pointer to an object
256  * @return @c pointer_traits<_Ptr>::to_address(__ptr) if that expression is
257  well-formed, otherwise @c to_address(__ptr.operator->())
258  * @ingroup pointer_abstractions
259  */
260  template<typename _Ptr>
261  constexpr auto
262  to_address(const _Ptr& __ptr) noexcept
263  { return std::__to_address(__ptr); }
264 #endif // C++2a
265 
266 _GLIBCXX_END_NAMESPACE_VERSION
267 } // namespace std
268 
269 #endif
270 
271 #endif
concepts
std::to_address
constexpr _Tp * to_address(_Tp *__ptr) noexcept
Obtain address referenced by a pointer to an object.
Definition: ptr_traits.h:250
std::__ptr_rebind
typename pointer_traits< _Ptr >::template rebind< _Tp > __ptr_rebind
Convenience alias for rebinding pointers.
Definition: ptr_traits.h:208
std::pointer_traits< _Tp * >::difference_type
ptrdiff_t difference_type
Type used to represent the difference between two pointers.
Definition: ptr_traits.h:201
move.h
std::pointer_traits
Uniform interface to all pointer-like types.
Definition: ptr_traits.h:184
std::to_address
constexpr auto to_address(const _Ptr &__ptr) noexcept
Obtain address referenced by a pointer to an object.
Definition: ptr_traits.h:262
std::addressof
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:138
std::pointer_traits< _Tp * >::pointer
_Tp * pointer
The pointer type.
Definition: ptr_traits.h:197
std::pointer_traits< _Tp * >::element_type
_Tp element_type
The type pointed to.
Definition: ptr_traits.h:199
std::pointer_traits< _Tp * >::rebind
_Up * rebind
A pointer to a different type.
Definition: ptr_traits.h:203
std
ISO C++ entities toplevel namespace is std.
std::is_function
is_function
Definition: type_traits:260
__gnu_debug
GNU debug classes for public use.
Definition: boost_concept_check.h:57