1 // Pointer Traits -*- C++ -*-
2
3 // Copyright (C) 2011-2022 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 # ifndef __cpp_lib_constexpr_memory
40 // Defined to a newer value in bits/unique_ptr.h for C++23
41 # define __cpp_lib_constexpr_memory 201811L
42 # endif
43 namespace __gnu_debug { struct _Safe_iterator_base; }
44 #endif
45
_GLIBCXX_VISIBILITY(default)46 namespace std _GLIBCXX_VISIBILITY(default)
47 {
48 _GLIBCXX_BEGIN_NAMESPACE_VERSION
49
50 /// @cond undocumented
51
52 class __undefined;
53
54 // For a specialization `SomeTemplate<T, Types...>` the member `type` is T,
55 // otherwise `type` is `__undefined`.
56 template<typename _Tp>
57 struct __get_first_arg
58 { using type = __undefined; };
59
60 template<template<typename, typename...> class _SomeTemplate, typename _Tp,
61 typename... _Types>
62 struct __get_first_arg<_SomeTemplate<_Tp, _Types...>>
63 { using type = _Tp; };
64
65 // For a specialization `SomeTemplate<T, Args...>` and a type `U` the member
66 // `type` is `SomeTemplate<U, Args...>`, otherwise there is no member `type`.
67 template<typename _Tp, typename _Up>
68 struct __replace_first_arg
69 { };
70
71 template<template<typename, typename...> class _SomeTemplate, typename _Up,
72 typename _Tp, typename... _Types>
73 struct __replace_first_arg<_SomeTemplate<_Tp, _Types...>, _Up>
74 { using type = _SomeTemplate<_Up, _Types...>; };
75
76 // Detect the element type of a pointer-like type.
77 template<typename _Ptr, typename = void>
78 struct __ptr_traits_elem : __get_first_arg<_Ptr>
79 { };
80
81 // Use _Ptr::element_type if is a valid type.
82 #if __cpp_concepts
83 template<typename _Ptr> requires requires { typename _Ptr::element_type; }
84 struct __ptr_traits_elem<_Ptr, void>
85 { using type = typename _Ptr::element_type; };
86 #else
87 template<typename _Ptr>
88 struct __ptr_traits_elem<_Ptr, __void_t<typename _Ptr::element_type>>
89 { using type = typename _Ptr::element_type; };
90 #endif
91
92 template<typename _Ptr>
93 using __ptr_traits_elem_t = typename __ptr_traits_elem<_Ptr>::type;
94
95 /// @endcond
96
97 // Define pointer_traits<P>::pointer_to.
98 template<typename _Ptr, typename _Elt, bool = is_void<_Elt>::value>
99 struct __ptr_traits_ptr_to
100 {
101 using pointer = _Ptr;
102 using element_type = _Elt;
103
104 /**
105 * @brief Obtain a pointer to an object
106 * @param __r A reference to an object of type `element_type`
107 * @return `pointer::pointer_to(__r)`
108 * @pre `pointer::pointer_to(__r)` is a valid expression.
109 */
110 static pointer
111 pointer_to(element_type& __r)
112 #if __cpp_lib_concepts
113 requires requires {
114 { pointer::pointer_to(__r) } -> convertible_to<pointer>;
115 }
116 #endif
117 { return pointer::pointer_to(__r); }
118 };
119
120 // Do not define pointer_traits<P>::pointer_to if element type is void.
121 template<typename _Ptr, typename _Elt>
122 struct __ptr_traits_ptr_to<_Ptr, _Elt, true>
123 { };
124
125 // Partial specialization defining pointer_traits<T*>::pointer_to(T&).
126 template<typename _Tp>
127 struct __ptr_traits_ptr_to<_Tp*, _Tp, false>
128 {
129 using pointer = _Tp*;
130 using element_type = _Tp;
131
132 /**
133 * @brief Obtain a pointer to an object
134 * @param __r A reference to an object of type `element_type`
135 * @return `addressof(__r)`
136 */
137 static _GLIBCXX20_CONSTEXPR pointer
138 pointer_to(element_type& __r) noexcept
139 { return std::addressof(__r); }
140 };
141
142 template<typename _Ptr, typename _Elt>
143 struct __ptr_traits_impl : __ptr_traits_ptr_to<_Ptr, _Elt>
144 {
145 private:
146 template<typename _Tp>
147 using __diff_t = typename _Tp::difference_type;
148
149 template<typename _Tp, typename _Up>
150 using __rebind = __type_identity<typename _Tp::template rebind<_Up>>;
151
152 public:
153 /// The pointer type.
154 using pointer = _Ptr;
155
156 /// The type pointed to.
157 using element_type = _Elt;
158
159 /// The type used to represent the difference between two pointers.
160 using difference_type = __detected_or_t<ptrdiff_t, __diff_t, _Ptr>;
161
162 /// A pointer to a different type.
163 template<typename _Up>
164 using rebind = typename __detected_or_t<__replace_first_arg<_Ptr, _Up>,
165 __rebind, _Ptr, _Up>::type;
166 };
167
168 // _GLIBCXX_RESOLVE_LIB_DEFECTS
169 // 3545. std::pointer_traits should be SFINAE-friendly
170 template<typename _Ptr>
171 struct __ptr_traits_impl<_Ptr, __undefined>
172 { };
173
174 /**
175 * @brief Uniform interface to all pointer-like types
176 * @headerfile memory
177 * @ingroup pointer_abstractions
178 * @since C++11
179 */
180 template<typename _Ptr>
181 struct pointer_traits : __ptr_traits_impl<_Ptr, __ptr_traits_elem_t<_Ptr>>
182 { };
183
184 /**
185 * @brief Partial specialization for built-in pointers.
186 * @headerfile memory
187 * @ingroup pointer_abstractions
188 * @since C++11
189 */
190 template<typename _Tp>
191 struct pointer_traits<_Tp*> : __ptr_traits_ptr_to<_Tp*, _Tp>
192 {
193 /// The pointer type
194 typedef _Tp* pointer;
195 /// The type pointed to
196 typedef _Tp element_type;
197 /// Type used to represent the difference between two pointers
198 typedef ptrdiff_t difference_type;
199 /// A pointer to a different type.
200 template<typename _Up> using rebind = _Up*;
201 };
202
203 /// Convenience alias for rebinding pointers.
204 template<typename _Ptr, typename _Tp>
205 using __ptr_rebind = typename pointer_traits<_Ptr>::template rebind<_Tp>;
206
207 template<typename _Tp>
208 constexpr _Tp*
209 __to_address(_Tp* __ptr) noexcept
210 {
211 static_assert(!std::is_function<_Tp>::value, "not a function pointer");
212 return __ptr;
213 }
214
215 #if __cplusplus <= 201703L
216 template<typename _Ptr>
217 constexpr typename std::pointer_traits<_Ptr>::element_type*
218 __to_address(const _Ptr& __ptr)
219 { return std::__to_address(__ptr.operator->()); }
220 #else
221 template<typename _Ptr>
222 constexpr auto
223 __to_address(const _Ptr& __ptr) noexcept
224 -> decltype(std::pointer_traits<_Ptr>::to_address(__ptr))
225 { return std::pointer_traits<_Ptr>::to_address(__ptr); }
226
227 template<typename _Ptr, typename... _None>
228 constexpr auto
229 __to_address(const _Ptr& __ptr, _None...) noexcept
230 {
231 if constexpr (is_base_of_v<__gnu_debug::_Safe_iterator_base, _Ptr>)
232 return std::__to_address(__ptr.base().operator->());
233 else
234 return std::__to_address(__ptr.operator->());
235 }
236
237 #define __cpp_lib_to_address 201711L
238
239 /**
240 * @brief Obtain address referenced by a pointer to an object
241 * @param __ptr A pointer to an object
242 * @return @c __ptr
243 * @ingroup pointer_abstractions
244 */
245 template<typename _Tp>
246 constexpr _Tp*
247 to_address(_Tp* __ptr) noexcept
248 { return std::__to_address(__ptr); }
249
250 /**
251 * @brief Obtain address referenced by a pointer to an object
252 * @param __ptr A pointer to an object
253 * @return @c pointer_traits<_Ptr>::to_address(__ptr) if that expression is
254 well-formed, otherwise @c to_address(__ptr.operator->())
255 * @ingroup pointer_abstractions
256 */
257 template<typename _Ptr>
258 constexpr auto
259 to_address(const _Ptr& __ptr) noexcept
260 { return std::__to_address(__ptr); }
261 #endif // C++2a
262
263 _GLIBCXX_END_NAMESPACE_VERSION
264 } // namespace std
265
266 #endif
267
268 #endif
269