libstdc++
any
Go to the documentation of this file.
1 // <experimental/any> -*- C++ -*-
2 
3 // Copyright (C) 2014-2018 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 experimental/any
26  * This is a TS C++ Library header.
27  */
28 
29 #ifndef _GLIBCXX_EXPERIMENTAL_ANY
30 #define _GLIBCXX_EXPERIMENTAL_ANY 1
31 
32 #pragma GCC system_header
33 
34 #if __cplusplus >= 201402L
35 
36 #include <typeinfo>
37 #include <new>
38 #include <utility>
39 #include <type_traits>
40 #include <experimental/bits/lfts_config.h>
41 
42 namespace std _GLIBCXX_VISIBILITY(default)
43 {
44 _GLIBCXX_BEGIN_NAMESPACE_VERSION
45 
46 namespace experimental
47 {
48 inline namespace fundamentals_v1
49 {
50  /**
51  * @defgroup any Type-safe container of any type
52  * @ingroup experimental
53  *
54  * A type-safe container for single values of value types, as
55  * described in n3804 "Any Library Proposal (Revision 3)".
56  *
57  * @{
58  */
59 
60 #define __cpp_lib_experimental_any 201411
61 
62  /**
63  * @brief Exception class thrown by a failed @c any_cast
64  * @ingroup exceptions
65  */
66  class bad_any_cast : public bad_cast
67  {
68  public:
69  virtual const char* what() const noexcept { return "bad any_cast"; }
70  };
71 
72  [[gnu::noreturn]] inline void __throw_bad_any_cast()
73  {
74 #if __cpp_exceptions
75  throw bad_any_cast{};
76 #else
77  __builtin_abort();
78 #endif
79  }
80 
81  /**
82  * @brief A type-safe container of any type.
83  *
84  * An @c any object's state is either empty or it stores a contained object
85  * of CopyConstructible type.
86  */
87  class any
88  {
89  // Holds either pointer to a heap object or the contained object itself.
90  union _Storage
91  {
92  // This constructor intentionally doesn't initialize anything.
93  _Storage() = default;
94 
95  // Prevent trivial copies of this type, buffer might hold a non-POD.
96  _Storage(const _Storage&) = delete;
97  _Storage& operator=(const _Storage&) = delete;
98 
99  void* _M_ptr;
100  aligned_storage<sizeof(_M_ptr), alignof(void*)>::type _M_buffer;
101  };
102 
103  template<typename _Tp, typename _Safe = is_nothrow_move_constructible<_Tp>,
104  bool _Fits = (sizeof(_Tp) <= sizeof(_Storage))
105  && (alignof(_Tp) <= alignof(_Storage))>
106  using _Internal = std::integral_constant<bool, _Safe::value && _Fits>;
107 
108  template<typename _Tp>
109  struct _Manager_internal; // uses small-object optimization
110 
111  template<typename _Tp>
112  struct _Manager_external; // creates contained object on the heap
113 
114  template<typename _Tp>
115  using _Manager = conditional_t<_Internal<_Tp>::value,
116  _Manager_internal<_Tp>,
117  _Manager_external<_Tp>>;
118 
119  template<typename _Tp, typename _Decayed = decay_t<_Tp>>
120  using _Decay = enable_if_t<!is_same<_Decayed, any>::value, _Decayed>;
121 
122  public:
123  // construct/destruct
124 
125  /// Default constructor, creates an empty object.
126  any() noexcept : _M_manager(nullptr) { }
127 
128  /// Copy constructor, copies the state of @p __other
129  any(const any& __other)
130  {
131  if (__other.empty())
132  _M_manager = nullptr;
133  else
134  {
135  _Arg __arg;
136  __arg._M_any = this;
137  __other._M_manager(_Op_clone, &__other, &__arg);
138  }
139  }
140 
141  /**
142  * @brief Move constructor, transfer the state from @p __other
143  *
144  * @post @c __other.empty() (this postcondition is a GNU extension)
145  */
146  any(any&& __other) noexcept
147  {
148  if (__other.empty())
149  _M_manager = nullptr;
150  else
151  {
152  _Arg __arg;
153  __arg._M_any = this;
154  __other._M_manager(_Op_xfer, &__other, &__arg);
155  }
156  }
157 
158  /// Construct with a copy of @p __value as the contained object.
159  template <typename _ValueType, typename _Tp = _Decay<_ValueType>,
160  typename _Mgr = _Manager<_Tp>,
161  typename enable_if<is_constructible<_Tp, _ValueType&&>::value,
162  bool>::type = true>
163  any(_ValueType&& __value)
164  : _M_manager(&_Mgr::_S_manage)
165  {
166  _Mgr::_S_create(_M_storage, std::forward<_ValueType>(__value));
167  static_assert(is_copy_constructible<_Tp>::value,
168  "The contained object must be CopyConstructible");
169  }
170 
171  /// Construct with a copy of @p __value as the contained object.
172  template <typename _ValueType, typename _Tp = _Decay<_ValueType>,
173  typename _Mgr = _Manager<_Tp>,
174  typename enable_if<!is_constructible<_Tp, _ValueType&&>::value,
175  bool>::type = false>
176  any(_ValueType&& __value)
177  : _M_manager(&_Mgr::_S_manage)
178  {
179  _Mgr::_S_create(_M_storage, __value);
180  static_assert(is_copy_constructible<_Tp>::value,
181  "The contained object must be CopyConstructible");
182  }
183 
184  /// Destructor, calls @c clear()
185  ~any() { clear(); }
186 
187  // assignments
188 
189  /// Copy the state of another object.
190  any& operator=(const any& __rhs)
191  {
192  *this = any(__rhs);
193  return *this;
194  }
195 
196  /**
197  * @brief Move assignment operator
198  *
199  * @post @c __rhs.empty() (not guaranteed for other implementations)
200  */
201  any& operator=(any&& __rhs) noexcept
202  {
203  if (__rhs.empty())
204  clear();
205  else if (this != &__rhs)
206  {
207  clear();
208  _Arg __arg;
209  __arg._M_any = this;
210  __rhs._M_manager(_Op_xfer, &__rhs, &__arg);
211  }
212  return *this;
213  }
214 
215  /// Store a copy of @p __rhs as the contained object.
216  template<typename _ValueType>
217  enable_if_t<!is_same<any, decay_t<_ValueType>>::value, any&>
218  operator=(_ValueType&& __rhs)
219  {
220  *this = any(std::forward<_ValueType>(__rhs));
221  return *this;
222  }
223 
224  // modifiers
225 
226  /// If not empty, destroy the contained object.
227  void clear() noexcept
228  {
229  if (!empty())
230  {
231  _M_manager(_Op_destroy, this, nullptr);
232  _M_manager = nullptr;
233  }
234  }
235 
236  /// Exchange state with another object.
237  void swap(any& __rhs) noexcept
238  {
239  if (empty() && __rhs.empty())
240  return;
241 
242  if (!empty() && !__rhs.empty())
243  {
244  if (this == &__rhs)
245  return;
246 
247  any __tmp;
248  _Arg __arg;
249  __arg._M_any = &__tmp;
250  __rhs._M_manager(_Op_xfer, &__rhs, &__arg);
251  __arg._M_any = &__rhs;
252  _M_manager(_Op_xfer, this, &__arg);
253  __arg._M_any = this;
254  __tmp._M_manager(_Op_xfer, &__tmp, &__arg);
255  }
256  else
257  {
258  any* __empty = empty() ? this : &__rhs;
259  any* __full = empty() ? &__rhs : this;
260  _Arg __arg;
261  __arg._M_any = __empty;
262  __full->_M_manager(_Op_xfer, __full, &__arg);
263  }
264  }
265 
266  // observers
267 
268  /// Reports whether there is a contained object or not.
269  bool empty() const noexcept { return _M_manager == nullptr; }
270 
271 #if __cpp_rtti
272  /// The @c typeid of the contained object, or @c typeid(void) if empty.
273  const type_info& type() const noexcept
274  {
275  if (empty())
276  return typeid(void);
277  _Arg __arg;
278  _M_manager(_Op_get_type_info, this, &__arg);
279  return *__arg._M_typeinfo;
280  }
281 #endif
282 
283  template<typename _Tp>
284  static constexpr bool __is_valid_cast()
285  { return __or_<is_reference<_Tp>, is_copy_constructible<_Tp>>::value; }
286 
287  private:
288  enum _Op {
289  _Op_access, _Op_get_type_info, _Op_clone, _Op_destroy, _Op_xfer
290  };
291 
292  union _Arg
293  {
294  void* _M_obj;
295  const std::type_info* _M_typeinfo;
296  any* _M_any;
297  };
298 
299  void (*_M_manager)(_Op, const any*, _Arg*);
300  _Storage _M_storage;
301 
302  template<typename _Tp>
303  friend void* __any_caster(const any* __any);
304 
305  // Manage in-place contained object.
306  template<typename _Tp>
307  struct _Manager_internal
308  {
309  static void
310  _S_manage(_Op __which, const any* __anyp, _Arg* __arg);
311 
312  template<typename _Up>
313  static void
314  _S_create(_Storage& __storage, _Up&& __value)
315  {
316  void* __addr = &__storage._M_buffer;
317  ::new (__addr) _Tp(std::forward<_Up>(__value));
318  }
319  };
320 
321  // Manage external contained object.
322  template<typename _Tp>
323  struct _Manager_external
324  {
325  static void
326  _S_manage(_Op __which, const any* __anyp, _Arg* __arg);
327 
328  template<typename _Up>
329  static void
330  _S_create(_Storage& __storage, _Up&& __value)
331  {
332  __storage._M_ptr = new _Tp(std::forward<_Up>(__value));
333  }
334  };
335  };
336 
337  /// Exchange the states of two @c any objects.
338  inline void swap(any& __x, any& __y) noexcept { __x.swap(__y); }
339 
340  /**
341  * @brief Access the contained object.
342  *
343  * @tparam _ValueType A const-reference or CopyConstructible type.
344  * @param __any The object to access.
345  * @return The contained object.
346  * @throw bad_any_cast If <code>
347  * __any.type() != typeid(remove_reference_t<_ValueType>)
348  * </code>
349  */
350  template<typename _ValueType>
351  inline _ValueType any_cast(const any& __any)
352  {
353  static_assert(any::__is_valid_cast<_ValueType>(),
354  "Template argument must be a reference or CopyConstructible type");
355  auto __p = any_cast<add_const_t<remove_reference_t<_ValueType>>>(&__any);
356  if (__p)
357  return *__p;
358  __throw_bad_any_cast();
359  }
360 
361  /**
362  * @brief Access the contained object.
363  *
364  * @tparam _ValueType A reference or CopyConstructible type.
365  * @param __any The object to access.
366  * @return The contained object.
367  * @throw bad_any_cast If <code>
368  * __any.type() != typeid(remove_reference_t<_ValueType>)
369  * </code>
370  *
371  * @{
372  */
373  template<typename _ValueType>
374  inline _ValueType any_cast(any& __any)
375  {
376  static_assert(any::__is_valid_cast<_ValueType>(),
377  "Template argument must be a reference or CopyConstructible type");
378  auto __p = any_cast<remove_reference_t<_ValueType>>(&__any);
379  if (__p)
380  return *__p;
381  __throw_bad_any_cast();
382  }
383 
384  template<typename _ValueType,
385  typename enable_if<!is_move_constructible<_ValueType>::value
386  || is_lvalue_reference<_ValueType>::value,
387  bool>::type = true>
388  inline _ValueType any_cast(any&& __any)
389  {
390  static_assert(any::__is_valid_cast<_ValueType>(),
391  "Template argument must be a reference or CopyConstructible type");
392  auto __p = any_cast<remove_reference_t<_ValueType>>(&__any);
393  if (__p)
394  return *__p;
395  __throw_bad_any_cast();
396  }
397 
398  template<typename _ValueType,
399  typename enable_if<is_move_constructible<_ValueType>::value
400  && !is_lvalue_reference<_ValueType>::value,
401  bool>::type = false>
402  inline _ValueType any_cast(any&& __any)
403  {
404  static_assert(any::__is_valid_cast<_ValueType>(),
405  "Template argument must be a reference or CopyConstructible type");
406  auto __p = any_cast<remove_reference_t<_ValueType>>(&__any);
407  if (__p)
408  return std::move(*__p);
409  __throw_bad_any_cast();
410  }
411  // @}
412 
413  template<typename _Tp>
414  void* __any_caster(const any* __any)
415  {
416  struct _None { };
417  using _Up = decay_t<_Tp>;
418  using _Vp = conditional_t<is_copy_constructible<_Up>::value, _Up, _None>;
419  if (__any->_M_manager != &any::_Manager<_Vp>::_S_manage)
420  return nullptr;
421  any::_Arg __arg;
422  __any->_M_manager(any::_Op_access, __any, &__arg);
423  return __arg._M_obj;
424  }
425 
426  /**
427  * @brief Access the contained object.
428  *
429  * @tparam _ValueType The type of the contained object.
430  * @param __any A pointer to the object to access.
431  * @return The address of the contained object if <code>
432  * __any != nullptr && __any.type() == typeid(_ValueType)
433  * </code>, otherwise a null pointer.
434  *
435  * @{
436  */
437  template<typename _ValueType>
438  inline const _ValueType* any_cast(const any* __any) noexcept
439  {
440  if (__any)
441  return static_cast<_ValueType*>(__any_caster<_ValueType>(__any));
442  return nullptr;
443  }
444 
445  template<typename _ValueType>
446  inline _ValueType* any_cast(any* __any) noexcept
447  {
448  if (__any)
449  return static_cast<_ValueType*>(__any_caster<_ValueType>(__any));
450  return nullptr;
451  }
452  // @}
453 
454  template<typename _Tp>
455  void
456  any::_Manager_internal<_Tp>::
457  _S_manage(_Op __which, const any* __any, _Arg* __arg)
458  {
459  // The contained object is in _M_storage._M_buffer
460  auto __ptr = reinterpret_cast<const _Tp*>(&__any->_M_storage._M_buffer);
461  switch (__which)
462  {
463  case _Op_access:
464  __arg->_M_obj = const_cast<_Tp*>(__ptr);
465  break;
466  case _Op_get_type_info:
467 #if __cpp_rtti
468  __arg->_M_typeinfo = &typeid(_Tp);
469 #endif
470  break;
471  case _Op_clone:
472  ::new(&__arg->_M_any->_M_storage._M_buffer) _Tp(*__ptr);
473  __arg->_M_any->_M_manager = __any->_M_manager;
474  break;
475  case _Op_destroy:
476  __ptr->~_Tp();
477  break;
478  case _Op_xfer:
479  ::new(&__arg->_M_any->_M_storage._M_buffer) _Tp
480  (std::move(*const_cast<_Tp*>(__ptr)));
481  __ptr->~_Tp();
482  __arg->_M_any->_M_manager = __any->_M_manager;
483  const_cast<any*>(__any)->_M_manager = nullptr;
484  break;
485  }
486  }
487 
488  template<typename _Tp>
489  void
490  any::_Manager_external<_Tp>::
491  _S_manage(_Op __which, const any* __any, _Arg* __arg)
492  {
493  // The contained object is *_M_storage._M_ptr
494  auto __ptr = static_cast<const _Tp*>(__any->_M_storage._M_ptr);
495  switch (__which)
496  {
497  case _Op_access:
498  __arg->_M_obj = const_cast<_Tp*>(__ptr);
499  break;
500  case _Op_get_type_info:
501 #if __cpp_rtti
502  __arg->_M_typeinfo = &typeid(_Tp);
503 #endif
504  break;
505  case _Op_clone:
506  __arg->_M_any->_M_storage._M_ptr = new _Tp(*__ptr);
507  __arg->_M_any->_M_manager = __any->_M_manager;
508  break;
509  case _Op_destroy:
510  delete __ptr;
511  break;
512  case _Op_xfer:
513  __arg->_M_any->_M_storage._M_ptr = __any->_M_storage._M_ptr;
514  __arg->_M_any->_M_manager = __any->_M_manager;
515  const_cast<any*>(__any)->_M_manager = nullptr;
516  break;
517  }
518  }
519 
520  // @} group any
521 } // namespace fundamentals_v1
522 } // namespace experimental
523 
524 _GLIBCXX_END_NAMESPACE_VERSION
525 } // namespace std
526 
527 #endif // C++14
528 
529 #endif // _GLIBCXX_EXPERIMENTAL_ANY