1// Pointer Traits -*- C++ -*-
2
3// Copyright (C) 2011-2021 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#define __cpp_lib_constexpr_memory 201811L
39namespace __gnu_debug { struct _Safe_iterator_base; }
40#endif
41
42namespace std _GLIBCXX_VISIBILITY(default)
43{
44_GLIBCXX_BEGIN_NAMESPACE_VERSION
45
46 class __undefined;
47
48 // Given Template<T, ...> return T, otherwise invalid.
49 template<typename _Tp>
50 struct __get_first_arg
51 { using type = __undefined; };
52
53 template<template<typename, typename...> class _Template, typename _Tp,
54 typename... _Types>
55 struct __get_first_arg<_Template<_Tp, _Types...>>
56 { using type = _Tp; };
57
58 template<typename _Tp>
59 using __get_first_arg_t = typename __get_first_arg<_Tp>::type;
60
61 // Given Template<T, ...> and U return Template<U, ...>, otherwise invalid.
62 template<typename _Tp, typename _Up>
63 struct __replace_first_arg
64 { };
65
66 template<template<typename, typename...> class _Template, typename _Up,
67 typename _Tp, typename... _Types>
68 struct __replace_first_arg<_Template<_Tp, _Types...>, _Up>
69 { using type = _Template<_Up, _Types...>; };
70
71 template<typename _Tp, typename _Up>
72 using __replace_first_arg_t = typename __replace_first_arg<_Tp, _Up>::type;
73
74 template<typename _Tp>
75 using __make_not_void
76 = typename conditional<is_void<_Tp>::value, __undefined, _Tp>::type;
77
78 /**
79 * @brief Uniform interface to all pointer-like types
80 * @ingroup pointer_abstractions
81 */
82 template<typename _Ptr>
83 struct pointer_traits
84 {
85 private:
86 template<typename _Tp>
87 using __element_type = typename _Tp::element_type;
88
89 template<typename _Tp>
90 using __difference_type = typename _Tp::difference_type;
91
92 template<typename _Tp, typename _Up, typename = void>
93 struct __rebind : __replace_first_arg<_Tp, _Up> { };
94
95 template<typename _Tp, typename _Up>
96 struct __rebind<_Tp, _Up, __void_t<typename _Tp::template rebind<_Up>>>
97 { using type = typename _Tp::template rebind<_Up>; };
98
99 public:
100 /// The pointer type.
101 using pointer = _Ptr;
102
103 /// The type pointed to.
104 using element_type
105 = __detected_or_t<__get_first_arg_t<_Ptr>, __element_type, _Ptr>;
106
107 /// The type used to represent the difference between two pointers.
108 using difference_type
109 = __detected_or_t<ptrdiff_t, __difference_type, _Ptr>;
110
111 /// A pointer to a different type.
112 template<typename _Up>
113 using rebind = typename __rebind<_Ptr, _Up>::type;
114
115 static _Ptr
116 pointer_to(__make_not_void<element_type>& __e)
117 { return _Ptr::pointer_to(__e); }
118
119 static_assert(!is_same<element_type, __undefined>::value,
120 "pointer type defines element_type or is like SomePointer<T, Args>");
121 };
122
123 /**
124 * @brief Partial specialization for built-in pointers.
125 * @ingroup pointer_abstractions
126 */
127 template<typename _Tp>
128 struct pointer_traits<_Tp*>
129 {
130 /// The pointer type
131 typedef _Tp* pointer;
132 /// The type pointed to
133 typedef _Tp element_type;
134 /// Type used to represent the difference between two pointers
135 typedef ptrdiff_t difference_type;
136
137 template<typename _Up>
138 using rebind = _Up*;
139
140 /**
141 * @brief Obtain a pointer to an object
142 * @param __r A reference to an object of type @c element_type
143 * @return @c addressof(__r)
144 */
145 static _GLIBCXX20_CONSTEXPR pointer
146 pointer_to(__make_not_void<element_type>& __r) noexcept
147 { return std::addressof(__r); }
148 };
149
150 /// Convenience alias for rebinding pointers.
151 template<typename _Ptr, typename _Tp>
152 using __ptr_rebind = typename pointer_traits<_Ptr>::template rebind<_Tp>;
153
154 template<typename _Tp>
155 constexpr _Tp*
156 __to_address(_Tp* __ptr) noexcept
157 {
158 static_assert(!std::is_function<_Tp>::value, "not a function pointer");
159 return __ptr;
160 }
161
162#if __cplusplus <= 201703L
163 template<typename _Ptr>
164 constexpr typename std::pointer_traits<_Ptr>::element_type*
165 __to_address(const _Ptr& __ptr)
166 { return std::__to_address(__ptr.operator->()); }
167#else
168 template<typename _Ptr>
169 constexpr auto
170 __to_address(const _Ptr& __ptr) noexcept
171 -> decltype(std::pointer_traits<_Ptr>::to_address(__ptr))
172 { return std::pointer_traits<_Ptr>::to_address(__ptr); }
173
174 template<typename _Ptr, typename... _None>
175 constexpr auto
176 __to_address(const _Ptr& __ptr, _None...) noexcept
177 {
178 if constexpr (is_base_of_v<__gnu_debug::_Safe_iterator_base, _Ptr>)
179 return std::__to_address(__ptr.base().operator->());
180 else
181 return std::__to_address(__ptr.operator->());
182 }
183
184#define __cpp_lib_to_address 201711L
185
186 /**
187 * @brief Obtain address referenced by a pointer to an object
188 * @param __ptr A pointer to an object
189 * @return @c __ptr
190 * @ingroup pointer_abstractions
191 */
192 template<typename _Tp>
193 constexpr _Tp*
194 to_address(_Tp* __ptr) noexcept
195 { return std::__to_address(__ptr); }
196
197 /**
198 * @brief Obtain address referenced by a pointer to an object
199 * @param __ptr A pointer to an object
200 * @return @c pointer_traits<_Ptr>::to_address(__ptr) if that expression is
201 well-formed, otherwise @c to_address(__ptr.operator->())
202 * @ingroup pointer_abstractions
203 */
204 template<typename _Ptr>
205 constexpr auto
206 to_address(const _Ptr& __ptr) noexcept
207 { return std::__to_address(__ptr); }
208#endif // C++2a
209
210_GLIBCXX_END_NAMESPACE_VERSION
211} // namespace std
212
213#endif
214
215#endif
216