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