libstdc++
any
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1// <any> -*- C++ -*-
2
3// Copyright (C) 2014-2020 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 include/any
26 * This is a Standard C++ Library header.
27 */
28
29#ifndef _GLIBCXX_ANY
30#define _GLIBCXX_ANY 1
31
32#pragma GCC system_header
33
34#if __cplusplus >= 201703L
35
36#include <typeinfo>
37#include <new>
38#include <utility>
39#include <type_traits>
40
41namespace std _GLIBCXX_VISIBILITY(default)
42{
43_GLIBCXX_BEGIN_NAMESPACE_VERSION
44
45 /**
46 * @addtogroup utilities
47 * @{
48 */
49
50 /**
51 * @brief Exception class thrown by a failed @c any_cast
52 * @ingroup exceptions
53 */
54 class bad_any_cast : public bad_cast
55 {
56 public:
57 virtual const char* what() const noexcept { return "bad any_cast"; }
58 };
59
60 [[gnu::noreturn]] inline void __throw_bad_any_cast()
61 {
62#if __cpp_exceptions
63 throw bad_any_cast{};
64#else
65 __builtin_abort();
66#endif
67 }
68
69#define __cpp_lib_any 201606L
70
71 /**
72 * @brief A type-safe container of any type.
73 *
74 * An @c any object's state is either empty or it stores a contained object
75 * of CopyConstructible type.
76 */
77 class any
78 {
79 // Holds either pointer to a heap object or the contained object itself.
80 union _Storage
81 {
82 constexpr _Storage() : _M_ptr{nullptr} {}
83
84 // Prevent trivial copies of this type, buffer might hold a non-POD.
85 _Storage(const _Storage&) = delete;
86 _Storage& operator=(const _Storage&) = delete;
87
88 void* _M_ptr;
89 aligned_storage<sizeof(_M_ptr), alignof(void*)>::type _M_buffer;
90 };
91
92 template<typename _Tp, typename _Safe = is_nothrow_move_constructible<_Tp>,
93 bool _Fits = (sizeof(_Tp) <= sizeof(_Storage))
94 && (alignof(_Tp) <= alignof(_Storage))>
95 using _Internal = std::integral_constant<bool, _Safe::value && _Fits>;
96
97 template<typename _Tp>
98 struct _Manager_internal; // uses small-object optimization
99
100 template<typename _Tp>
101 struct _Manager_external; // creates contained object on the heap
102
103 template<typename _Tp>
104 using _Manager = conditional_t<_Internal<_Tp>::value,
105 _Manager_internal<_Tp>,
106 _Manager_external<_Tp>>;
107
108 template<typename _Tp, typename _VTp = decay_t<_Tp>>
109 using _Decay_if_not_any = enable_if_t<!is_same_v<_VTp, any>, _VTp>;
110
111 /// Emplace with an object created from @p __args as the contained object.
112 template <typename _Tp, typename... _Args,
113 typename _Mgr = _Manager<_Tp>>
114 void __do_emplace(_Args&&... __args)
115 {
116 reset();
117 _Mgr::_S_create(_M_storage, std::forward<_Args>(__args)...);
118 _M_manager = &_Mgr::_S_manage;
119 }
120
121 /// Emplace with an object created from @p __il and @p __args as
122 /// the contained object.
123 template <typename _Tp, typename _Up, typename... _Args,
124 typename _Mgr = _Manager<_Tp>>
125 void __do_emplace(initializer_list<_Up> __il, _Args&&... __args)
126 {
127 reset();
128 _Mgr::_S_create(_M_storage, __il, std::forward<_Args>(__args)...);
129 _M_manager = &_Mgr::_S_manage;
130 }
131
132 template <typename _Res, typename _Tp, typename... _Args>
133 using __any_constructible
134 = enable_if<__and_<is_copy_constructible<_Tp>,
135 is_constructible<_Tp, _Args...>>::value,
136 _Res>;
137
138 template <typename _Tp, typename... _Args>
139 using __any_constructible_t
140 = typename __any_constructible<bool, _Tp, _Args...>::type;
141
142 template<typename _VTp, typename... _Args>
143 using __emplace_t
144 = typename __any_constructible<_VTp&, _VTp, _Args...>::type;
145
146 public:
147 // construct/destruct
148
149 /// Default constructor, creates an empty object.
150 constexpr any() noexcept : _M_manager(nullptr) { }
151
152 /// Copy constructor, copies the state of @p __other
153 any(const any& __other)
154 {
155 if (!__other.has_value())
156 _M_manager = nullptr;
157 else
158 {
159 _Arg __arg;
160 __arg._M_any = this;
161 __other._M_manager(_Op_clone, &__other, &__arg);
162 }
163 }
164
165 /**
166 * @brief Move constructor, transfer the state from @p __other
167 *
168 * @post @c !__other.has_value() (this postcondition is a GNU extension)
169 */
170 any(any&& __other) noexcept
171 {
172 if (!__other.has_value())
173 _M_manager = nullptr;
174 else
175 {
176 _Arg __arg;
177 __arg._M_any = this;
178 __other._M_manager(_Op_xfer, &__other, &__arg);
179 }
180 }
181
182 /// Construct with a copy of @p __value as the contained object.
183 template <typename _Tp, typename _VTp = _Decay_if_not_any<_Tp>,
184 typename _Mgr = _Manager<_VTp>,
185 enable_if_t<is_copy_constructible<_VTp>::value
186 && !__is_in_place_type<_VTp>::value, bool> = true>
187 any(_Tp&& __value)
188 : _M_manager(&_Mgr::_S_manage)
189 {
190 _Mgr::_S_create(_M_storage, std::forward<_Tp>(__value));
191 }
192
193 /// Construct with an object created from @p __args as the contained object.
194 template <typename _Tp, typename... _Args, typename _VTp = decay_t<_Tp>,
195 typename _Mgr = _Manager<_VTp>,
196 __any_constructible_t<_VTp, _Args&&...> = false>
197 explicit
198 any(in_place_type_t<_Tp>, _Args&&... __args)
199 : _M_manager(&_Mgr::_S_manage)
200 {
201 _Mgr::_S_create(_M_storage, std::forward<_Args>(__args)...);
202 }
203
204 /// Construct with an object created from @p __il and @p __args as
205 /// the contained object.
206 template <typename _Tp, typename _Up, typename... _Args,
207 typename _VTp = decay_t<_Tp>, typename _Mgr = _Manager<_VTp>,
208 __any_constructible_t<_VTp, initializer_list<_Up>&,
209 _Args&&...> = false>
210 explicit
211 any(in_place_type_t<_Tp>, initializer_list<_Up> __il, _Args&&... __args)
212 : _M_manager(&_Mgr::_S_manage)
213 {
214 _Mgr::_S_create(_M_storage, __il, std::forward<_Args>(__args)...);
215 }
216
217 /// Destructor, calls @c reset()
218 ~any() { reset(); }
219
220 // assignments
221
222 /// Copy the state of another object.
223 any&
224 operator=(const any& __rhs)
225 {
226 *this = any(__rhs);
227 return *this;
228 }
229
230 /**
231 * @brief Move assignment operator
232 *
233 * @post @c !__rhs.has_value() (not guaranteed for other implementations)
234 */
235 any&
236 operator=(any&& __rhs) noexcept
237 {
238 if (!__rhs.has_value())
239 reset();
240 else if (this != &__rhs)
241 {
242 reset();
243 _Arg __arg;
244 __arg._M_any = this;
245 __rhs._M_manager(_Op_xfer, &__rhs, &__arg);
246 }
247 return *this;
248 }
249
250 /// Store a copy of @p __rhs as the contained object.
251 template<typename _Tp>
252 enable_if_t<is_copy_constructible<_Decay_if_not_any<_Tp>>::value, any&>
253 operator=(_Tp&& __rhs)
254 {
255 *this = any(std::forward<_Tp>(__rhs));
256 return *this;
257 }
258
259 /// Emplace with an object created from @p __args as the contained object.
260 template <typename _Tp, typename... _Args>
261 __emplace_t<decay_t<_Tp>, _Args...>
262 emplace(_Args&&... __args)
263 {
264 using _VTp = decay_t<_Tp>;
265 __do_emplace<_VTp>(std::forward<_Args>(__args)...);
266 any::_Arg __arg;
267 this->_M_manager(any::_Op_access, this, &__arg);
268 return *static_cast<_VTp*>(__arg._M_obj);
269 }
270
271 /// Emplace with an object created from @p __il and @p __args as
272 /// the contained object.
273 template <typename _Tp, typename _Up, typename... _Args>
274 __emplace_t<decay_t<_Tp>, initializer_list<_Up>&, _Args&&...>
275 emplace(initializer_list<_Up> __il, _Args&&... __args)
276 {
277 using _VTp = decay_t<_Tp>;
278 __do_emplace<_VTp, _Up>(__il, std::forward<_Args>(__args)...);
279 any::_Arg __arg;
280 this->_M_manager(any::_Op_access, this, &__arg);
281 return *static_cast<_VTp*>(__arg._M_obj);
282 }
283
284 // modifiers
285
286 /// If not empty, destroy the contained object.
287 void reset() noexcept
288 {
289 if (has_value())
290 {
291 _M_manager(_Op_destroy, this, nullptr);
292 _M_manager = nullptr;
293 }
294 }
295
296 /// Exchange state with another object.
297 void swap(any& __rhs) noexcept
298 {
299 if (!has_value() && !__rhs.has_value())
300 return;
301
302 if (has_value() && __rhs.has_value())
303 {
304 if (this == &__rhs)
305 return;
306
307 any __tmp;
308 _Arg __arg;
309 __arg._M_any = &__tmp;
310 __rhs._M_manager(_Op_xfer, &__rhs, &__arg);
311 __arg._M_any = &__rhs;
312 _M_manager(_Op_xfer, this, &__arg);
313 __arg._M_any = this;
314 __tmp._M_manager(_Op_xfer, &__tmp, &__arg);
315 }
316 else
317 {
318 any* __empty = !has_value() ? this : &__rhs;
319 any* __full = !has_value() ? &__rhs : this;
320 _Arg __arg;
321 __arg._M_any = __empty;
322 __full->_M_manager(_Op_xfer, __full, &__arg);
323 }
324 }
325
326 // observers
327
328 /// Reports whether there is a contained object or not.
329 bool has_value() const noexcept { return _M_manager != nullptr; }
330
331#if __cpp_rtti
332 /// The @c typeid of the contained object, or @c typeid(void) if empty.
333 const type_info& type() const noexcept
334 {
335 if (!has_value())
336 return typeid(void);
337 _Arg __arg;
338 _M_manager(_Op_get_type_info, this, &__arg);
339 return *__arg._M_typeinfo;
340 }
341#endif
342
343 template<typename _Tp>
344 static constexpr bool __is_valid_cast()
345 { return __or_<is_reference<_Tp>, is_copy_constructible<_Tp>>::value; }
346
347 private:
348 enum _Op {
349 _Op_access, _Op_get_type_info, _Op_clone, _Op_destroy, _Op_xfer
350 };
351
352 union _Arg
353 {
354 void* _M_obj;
355 const std::type_info* _M_typeinfo;
356 any* _M_any;
357 };
358
359 void (*_M_manager)(_Op, const any*, _Arg*);
360 _Storage _M_storage;
361
362 template<typename _Tp>
363 friend void* __any_caster(const any* __any);
364
365 // Manage in-place contained object.
366 template<typename _Tp>
367 struct _Manager_internal
368 {
369 static void
370 _S_manage(_Op __which, const any* __anyp, _Arg* __arg);
371
372 template<typename _Up>
373 static void
374 _S_create(_Storage& __storage, _Up&& __value)
375 {
376 void* __addr = &__storage._M_buffer;
377 ::new (__addr) _Tp(std::forward<_Up>(__value));
378 }
379
380 template<typename... _Args>
381 static void
382 _S_create(_Storage& __storage, _Args&&... __args)
383 {
384 void* __addr = &__storage._M_buffer;
385 ::new (__addr) _Tp(std::forward<_Args>(__args)...);
386 }
387 };
388
389 // Manage external contained object.
390 template<typename _Tp>
391 struct _Manager_external
392 {
393 static void
394 _S_manage(_Op __which, const any* __anyp, _Arg* __arg);
395
396 template<typename _Up>
397 static void
398 _S_create(_Storage& __storage, _Up&& __value)
399 {
400 __storage._M_ptr = new _Tp(std::forward<_Up>(__value));
401 }
402 template<typename... _Args>
403 static void
404 _S_create(_Storage& __storage, _Args&&... __args)
405 {
406 __storage._M_ptr = new _Tp(std::forward<_Args>(__args)...);
407 }
408 };
409 };
410
411 /// Exchange the states of two @c any objects.
412 inline void swap(any& __x, any& __y) noexcept { __x.swap(__y); }
413
414 /// Create an `any` holding a `_Tp` constructed from `__args...`.
415 template <typename _Tp, typename... _Args>
416 inline
417 enable_if_t<is_constructible_v<any, in_place_type_t<_Tp>, _Args...>, any>
418 make_any(_Args&&... __args)
419 {
420 return any(in_place_type<_Tp>, std::forward<_Args>(__args)...);
421 }
422
423 /// Create an `any` holding a `_Tp` constructed from `__il` and `__args...`.
424 template <typename _Tp, typename _Up, typename... _Args>
425 inline
426 enable_if_t<is_constructible_v<any, in_place_type_t<_Tp>,
427 initializer_list<_Up>&, _Args...>, any>
428 make_any(initializer_list<_Up> __il, _Args&&... __args)
429 {
430 return any(in_place_type<_Tp>, __il, std::forward<_Args>(__args)...);
431 }
432
433 /**
434 * @brief Access the contained object.
435 *
436 * @tparam _ValueType A const-reference or CopyConstructible type.
437 * @param __any The object to access.
438 * @return The contained object.
439 * @throw bad_any_cast If <code>
440 * __any.type() != typeid(remove_reference_t<_ValueType>)
441 * </code>
442 */
443 template<typename _ValueType>
444 inline _ValueType any_cast(const any& __any)
445 {
446 using _Up = __remove_cvref_t<_ValueType>;
447 static_assert(any::__is_valid_cast<_ValueType>(),
448 "Template argument must be a reference or CopyConstructible type");
449 static_assert(is_constructible_v<_ValueType, const _Up&>,
450 "Template argument must be constructible from a const value.");
451 auto __p = any_cast<_Up>(&__any);
452 if (__p)
453 return static_cast<_ValueType>(*__p);
454 __throw_bad_any_cast();
455 }
456
457 /**
458 * @brief Access the contained object.
459 *
460 * @tparam _ValueType A reference or CopyConstructible type.
461 * @param __any The object to access.
462 * @return The contained object.
463 * @throw bad_any_cast If <code>
464 * __any.type() != typeid(remove_reference_t<_ValueType>)
465 * </code>
466 *
467 * @{
468 */
469 template<typename _ValueType>
470 inline _ValueType any_cast(any& __any)
471 {
472 using _Up = __remove_cvref_t<_ValueType>;
473 static_assert(any::__is_valid_cast<_ValueType>(),
474 "Template argument must be a reference or CopyConstructible type");
475 static_assert(is_constructible_v<_ValueType, _Up&>,
476 "Template argument must be constructible from an lvalue.");
477 auto __p = any_cast<_Up>(&__any);
478 if (__p)
479 return static_cast<_ValueType>(*__p);
480 __throw_bad_any_cast();
481 }
482
483 template<typename _ValueType>
484 inline _ValueType any_cast(any&& __any)
485 {
486 using _Up = __remove_cvref_t<_ValueType>;
487 static_assert(any::__is_valid_cast<_ValueType>(),
488 "Template argument must be a reference or CopyConstructible type");
489 static_assert(is_constructible_v<_ValueType, _Up>,
490 "Template argument must be constructible from an rvalue.");
491 auto __p = any_cast<_Up>(&__any);
492 if (__p)
493 return static_cast<_ValueType>(std::move(*__p));
494 __throw_bad_any_cast();
495 }
496 /// @}
497
498 /// @cond undocumented
499 template<typename _Tp>
500 void* __any_caster(const any* __any)
501 {
502 // any_cast<T> returns non-null if __any->type() == typeid(T) and
503 // typeid(T) ignores cv-qualifiers so remove them:
504 using _Up = remove_cv_t<_Tp>;
505 // The contained value has a decayed type, so if decay_t<U> is not U,
506 // then it's not possible to have a contained value of type U:
507 if constexpr (!is_same_v<decay_t<_Up>, _Up>)
508 return nullptr;
509 // Only copy constructible types can be used for contained values:
510 else if constexpr (!is_copy_constructible_v<_Up>)
511 return nullptr;
512 // First try comparing function addresses, which works without RTTI
513 else if (__any->_M_manager == &any::_Manager<_Up>::_S_manage
514#if __cpp_rtti
515 || __any->type() == typeid(_Tp)
516#endif
517 )
518 {
519 any::_Arg __arg;
520 __any->_M_manager(any::_Op_access, __any, &__arg);
521 return __arg._M_obj;
522 }
523 return nullptr;
524 }
525 /// @endcond
526
527 /**
528 * @brief Access the contained object.
529 *
530 * @tparam _ValueType The type of the contained object.
531 * @param __any A pointer to the object to access.
532 * @return The address of the contained object if <code>
533 * __any != nullptr && __any.type() == typeid(_ValueType)
534 * </code>, otherwise a null pointer.
535 *
536 * @{
537 */
538 template<typename _ValueType>
539 inline const _ValueType* any_cast(const any* __any) noexcept
540 {
541 if constexpr (is_object_v<_ValueType>)
542 if (__any)
543 return static_cast<_ValueType*>(__any_caster<_ValueType>(__any));
544 return nullptr;
545 }
546
547 template<typename _ValueType>
548 inline _ValueType* any_cast(any* __any) noexcept
549 {
550 if constexpr (is_object_v<_ValueType>)
551 if (__any)
552 return static_cast<_ValueType*>(__any_caster<_ValueType>(__any));
553 return nullptr;
554 }
555 /// @}
556
557 template<typename _Tp>
558 void
559 any::_Manager_internal<_Tp>::
560 _S_manage(_Op __which, const any* __any, _Arg* __arg)
561 {
562 // The contained object is in _M_storage._M_buffer
563 auto __ptr = reinterpret_cast<const _Tp*>(&__any->_M_storage._M_buffer);
564 switch (__which)
565 {
566 case _Op_access:
567 __arg->_M_obj = const_cast<_Tp*>(__ptr);
568 break;
569 case _Op_get_type_info:
570#if __cpp_rtti
571 __arg->_M_typeinfo = &typeid(_Tp);
572#endif
573 break;
574 case _Op_clone:
575 ::new(&__arg->_M_any->_M_storage._M_buffer) _Tp(*__ptr);
576 __arg->_M_any->_M_manager = __any->_M_manager;
577 break;
578 case _Op_destroy:
579 __ptr->~_Tp();
580 break;
581 case _Op_xfer:
582 ::new(&__arg->_M_any->_M_storage._M_buffer) _Tp
583 (std::move(*const_cast<_Tp*>(__ptr)));
584 __ptr->~_Tp();
585 __arg->_M_any->_M_manager = __any->_M_manager;
586 const_cast<any*>(__any)->_M_manager = nullptr;
587 break;
588 }
589 }
590
591 template<typename _Tp>
592 void
593 any::_Manager_external<_Tp>::
594 _S_manage(_Op __which, const any* __any, _Arg* __arg)
595 {
596 // The contained object is *_M_storage._M_ptr
597 auto __ptr = static_cast<const _Tp*>(__any->_M_storage._M_ptr);
598 switch (__which)
599 {
600 case _Op_access:
601 __arg->_M_obj = const_cast<_Tp*>(__ptr);
602 break;
603 case _Op_get_type_info:
604#if __cpp_rtti
605 __arg->_M_typeinfo = &typeid(_Tp);
606#endif
607 break;
608 case _Op_clone:
609 __arg->_M_any->_M_storage._M_ptr = new _Tp(*__ptr);
610 __arg->_M_any->_M_manager = __any->_M_manager;
611 break;
612 case _Op_destroy:
613 delete __ptr;
614 break;
615 case _Op_xfer:
616 __arg->_M_any->_M_storage._M_ptr = __any->_M_storage._M_ptr;
617 __arg->_M_any->_M_manager = __any->_M_manager;
618 const_cast<any*>(__any)->_M_manager = nullptr;
619 break;
620 }
621 }
622
623 /// @}
624
625 namespace __detail::__variant
626 {
627 template<typename> struct _Never_valueless_alt; // see <variant>
628
629 // Provide the strong exception-safety guarantee when emplacing an
630 // any into a variant.
631 template<>
632 struct _Never_valueless_alt<std::any>
633 : std::true_type
634 { };
635 } // namespace __detail::__variant
636
637_GLIBCXX_END_NAMESPACE_VERSION
638} // namespace std
639
640#endif // C++17
641#endif // _GLIBCXX_ANY