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>
39namespace __gnu_debug { struct _Safe_iterator_base; }
40#endif
41
42namespace 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
263