1 // Implementation of std::move_only_function -*- C++ -*-
2
3 // Copyright The GNU Toolchain Authors.
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 include/bits/move_only_function.h
26 * This is an internal header file, included by other library headers.
27 * Do not attempt to use it directly. @headername{functional}
28 */
29
30 #ifndef _GLIBCXX_MOVE_ONLY_FUNCTION_H
31 #define _GLIBCXX_MOVE_ONLY_FUNCTION_H 1
32
33 #pragma GCC system_header
34
35 #if __cplusplus > 202002L
36
37 #include <bits/invoke.h>
38 #include <bits/utility.h>
39
40 namespace std _GLIBCXX_VISIBILITY(default)
41 {
42 _GLIBCXX_BEGIN_NAMESPACE_VERSION
43
44 #define __cpp_lib_move_only_function 202110L
45
46 template<typename... _Signature>
47 class move_only_function; // not defined
48
49 /// @cond undocumented
50 class _Mofunc_base
51 {
52 protected:
53 _Mofunc_base() noexcept
54 : _M_manage(_S_empty)
55 { }
56
57 _Mofunc_base(_Mofunc_base&& __x) noexcept
58 {
59 _M_manage = std::__exchange(__x._M_manage, _S_empty);
60 _M_manage(_M_storage, &__x._M_storage);
61 }
62
63 template<typename _Tp, typename... _Args>
64 static constexpr bool
65 _S_nothrow_init() noexcept
66 {
67 if constexpr (__stored_locally<_Tp>)
68 return is_nothrow_constructible_v<_Tp, _Args...>;
69 return false;
70 }
71
72 template<typename _Tp, typename... _Args>
73 void
74 _M_init(_Args&&... __args) noexcept(_S_nothrow_init<_Tp, _Args...>())
75 {
76 if constexpr (__stored_locally<_Tp>)
77 ::new (_M_storage._M_addr()) _Tp(std::forward<_Args>(__args)...);
78 else
79 _M_storage._M_p = new _Tp(std::forward<_Args>(__args)...);
80
81 _M_manage = &_S_manage<_Tp>;
82 }
83
84 _Mofunc_base&
85 operator=(_Mofunc_base&& __x) noexcept
86 {
87 _M_manage(_M_storage, nullptr);
88 _M_manage = std::__exchange(__x._M_manage, _S_empty);
89 _M_manage(_M_storage, &__x._M_storage);
90 return *this;
91 }
92
93 _Mofunc_base&
94 operator=(nullptr_t) noexcept
95 {
96 _M_manage(_M_storage, nullptr);
97 _M_manage = _S_empty;
98 return *this;
99 }
100
101 ~_Mofunc_base() { _M_manage(_M_storage, nullptr); }
102
103 void
104 swap(_Mofunc_base& __x) noexcept
105 {
106 // Order of operations here is more efficient if __x is empty.
107 _Storage __s;
108 __x._M_manage(__s, &__x._M_storage);
109 _M_manage(__x._M_storage, &_M_storage);
110 __x._M_manage(_M_storage, &__s);
111 std::swap(_M_manage, __x._M_manage);
112 }
113
114 template<typename _Tp, typename _Self>
115 static _Tp*
116 _S_access(_Self* __self) noexcept
117 {
118 if constexpr (__stored_locally<remove_const_t<_Tp>>)
119 return static_cast<_Tp*>(__self->_M_storage._M_addr());
120 else
121 return static_cast<_Tp*>(__self->_M_storage._M_p);
122 }
123
124 private:
125 struct _Storage
126 {
127 void* _M_addr() noexcept { return &_M_bytes[0]; }
128 const void* _M_addr() const noexcept { return &_M_bytes[0]; }
129
130 // We want to have enough space to store a simple delegate type.
131 struct _Delegate { void (_Storage::*__pfm)(); _Storage* __obj; };
132 union {
133 void* _M_p;
134 alignas(_Delegate) alignas(void(*)())
135 unsigned char _M_bytes[sizeof(_Delegate)];
136 };
137 };
138
139 template<typename _Tp>
140 static constexpr bool __stored_locally
141 = sizeof(_Tp) <= sizeof(_Storage) && alignof(_Tp) <= alignof(_Storage)
142 && is_nothrow_move_constructible_v<_Tp>;
143
144 // A function that either destroys the target object stored in __target,
145 // or moves the target object from *__src to __target.
146 using _Manager = void (*)(_Storage& __target, _Storage* __src) noexcept;
147
148 // The no-op manager function for objects with no target.
149 static void _S_empty(_Storage&, _Storage*) noexcept { }
150
151 // The real manager function for a target object of type _Tp.
152 template<typename _Tp>
153 static void
154 _S_manage(_Storage& __target, _Storage* __src) noexcept
155 {
156 if constexpr (__stored_locally<_Tp>)
157 {
158 if (__src)
159 {
160 _Tp* __rval = static_cast<_Tp*>(__src->_M_addr());
161 ::new (__target._M_addr()) _Tp(std::move(*__rval));
162 __rval->~_Tp();
163 }
164 else
165 static_cast<_Tp*>(__target._M_addr())->~_Tp();
166 }
167 else
168 {
169 if (__src)
170 __target._M_p = __src->_M_p;
171 else
172 delete static_cast<_Tp*>(__target._M_p);
173 }
174 }
175
176 _Storage _M_storage;
177 _Manager _M_manage;
178 };
179
180 template<typename _Tp>
181 inline constexpr bool __is_move_only_function_v = false;
182 template<typename _Tp>
183 constexpr bool __is_move_only_function_v<move_only_function<_Tp>> = true;
184 /// @endcond
185
186 namespace __detail::__variant
187 {
188 template<typename> struct _Never_valueless_alt; // see <variant>
189
190 // Provide the strong exception-safety guarantee when emplacing a
191 // move_only_function into a variant.
192 template<typename... _Signature>
193 struct _Never_valueless_alt<std::move_only_function<_Signature...>>
194 : true_type
195 { };
196 } // namespace __detail::__variant
197
198 _GLIBCXX_END_NAMESPACE_VERSION
199 } // namespace std
200
201 #include "mofunc_impl.h"
202 #define _GLIBCXX_MOF_CV const
203 #include "mofunc_impl.h"
204 #define _GLIBCXX_MOF_REF &
205 #include "mofunc_impl.h"
206 #define _GLIBCXX_MOF_REF &&
207 #include "mofunc_impl.h"
208 #define _GLIBCXX_MOF_CV const
209 #define _GLIBCXX_MOF_REF &
210 #include "mofunc_impl.h"
211 #define _GLIBCXX_MOF_CV const
212 #define _GLIBCXX_MOF_REF &&
213 #include "mofunc_impl.h"
214
215 #endif // C++23
216 #endif // _GLIBCXX_MOVE_ONLY_FUNCTION_H