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