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 return *any::_Manager<_VTp>::_S_access(_M_storage);
267 }
268
269 /// Emplace with an object created from @p __il and @p __args as
270 /// the contained object.
271 template <typename _Tp, typename _Up, typename... _Args>
272 __emplace_t<decay_t<_Tp>, initializer_list<_Up>&, _Args&&...>
273 emplace(initializer_list<_Up> __il, _Args&&... __args)
274 {
275 using _VTp = decay_t<_Tp>;
276 __do_emplace<_VTp, _Up>(__il, std::forward<_Args>(__args)...);
277 return *any::_Manager<_VTp>::_S_access(_M_storage);
278 }
279
280 // modifiers
281
282 /// If not empty, destroy the contained object.
283 void reset() noexcept
284 {
285 if (has_value())
286 {
287 _M_manager(_Op_destroy, this, nullptr);
288 _M_manager = nullptr;
289 }
290 }
291
292 /// Exchange state with another object.
293 void swap(any& __rhs) noexcept
294 {
295 if (!has_value() && !__rhs.has_value())
296 return;
297
298 if (has_value() && __rhs.has_value())
299 {
300 if (this == &__rhs)
301 return;
302
303 any __tmp;
304 _Arg __arg;
305 __arg._M_any = &__tmp;
306 __rhs._M_manager(_Op_xfer, &__rhs, &__arg);
307 __arg._M_any = &__rhs;
308 _M_manager(_Op_xfer, this, &__arg);
309 __arg._M_any = this;
310 __tmp._M_manager(_Op_xfer, &__tmp, &__arg);
311 }
312 else
313 {
314 any* __empty = !has_value() ? this : &__rhs;
315 any* __full = !has_value() ? &__rhs : this;
316 _Arg __arg;
317 __arg._M_any = __empty;
318 __full->_M_manager(_Op_xfer, __full, &__arg);
319 }
320 }
321
322 // observers
323
324 /// Reports whether there is a contained object or not.
325 bool has_value() const noexcept { return _M_manager != nullptr; }
326
327#if __cpp_rtti
328 /// The @c typeid of the contained object, or @c typeid(void) if empty.
329 const type_info& type() const noexcept
330 {
331 if (!has_value())
332 return typeid(void);
333 _Arg __arg;
334 _M_manager(_Op_get_type_info, this, &__arg);
335 return *__arg._M_typeinfo;
336 }
337#endif
338
339 template<typename _Tp>
340 static constexpr bool __is_valid_cast()
341 { return __or_<is_reference<_Tp>, is_copy_constructible<_Tp>>::value; }
342
343 private:
344 enum _Op {
345 _Op_access, _Op_get_type_info, _Op_clone, _Op_destroy, _Op_xfer
346 };
347
348 union _Arg
349 {
350 void* _M_obj;
351 const std::type_info* _M_typeinfo;
352 any* _M_any;
353 };
354
355 void (*_M_manager)(_Op, const any*, _Arg*);
356 _Storage _M_storage;
357
358 template<typename _Tp>
359 friend void* __any_caster(const any* __any);
360
361 // Manage in-place contained object.
362 template<typename _Tp>
363 struct _Manager_internal
364 {
365 static void
366 _S_manage(_Op __which, const any* __anyp, _Arg* __arg);
367
368 template<typename _Up>
369 static void
370 _S_create(_Storage& __storage, _Up&& __value)
371 {
372 void* __addr = &__storage._M_buffer;
373 ::new (__addr) _Tp(std::forward<_Up>(__value));
374 }
375
376 template<typename... _Args>
377 static void
378 _S_create(_Storage& __storage, _Args&&... __args)
379 {
380 void* __addr = &__storage._M_buffer;
381 ::new (__addr) _Tp(std::forward<_Args>(__args)...);
382 }
383
384 static _Tp*
385 _S_access(const _Storage& __storage)
386 {
387 // The contained object is in __storage._M_buffer
388 const void* __addr = &__storage._M_buffer;
389 return static_cast<_Tp*>(const_cast<void*>(__addr));
390 }
391 };
392
393 // Manage external contained object.
394 template<typename _Tp>
395 struct _Manager_external
396 {
397 static void
398 _S_manage(_Op __which, const any* __anyp, _Arg* __arg);
399
400 template<typename _Up>
401 static void
402 _S_create(_Storage& __storage, _Up&& __value)
403 {
404 __storage._M_ptr = new _Tp(std::forward<_Up>(__value));
405 }
406 template<typename... _Args>
407 static void
408 _S_create(_Storage& __storage, _Args&&... __args)
409 {
410 __storage._M_ptr = new _Tp(std::forward<_Args>(__args)...);
411 }
412 static _Tp*
413 _S_access(const _Storage& __storage)
414 {
415 // The contained object is in *__storage._M_ptr
416 return static_cast<_Tp*>(__storage._M_ptr);
417 }
418 };
419 };
420
421 /// Exchange the states of two @c any objects.
422 inline void swap(any& __x, any& __y) noexcept { __x.swap(__y); }
423
424 /// Create an `any` holding a `_Tp` constructed from `__args...`.
425 template <typename _Tp, typename... _Args>
426 inline
427 enable_if_t<is_constructible_v<any, in_place_type_t<_Tp>, _Args...>, any>
428 make_any(_Args&&... __args)
429 {
430 return any(in_place_type<_Tp>, std::forward<_Args>(__args)...);
431 }
432
433 /// Create an `any` holding a `_Tp` constructed from `__il` and `__args...`.
434 template <typename _Tp, typename _Up, typename... _Args>
435 inline
436 enable_if_t<is_constructible_v<any, in_place_type_t<_Tp>,
437 initializer_list<_Up>&, _Args...>, any>
438 make_any(initializer_list<_Up> __il, _Args&&... __args)
439 {
440 return any(in_place_type<_Tp>, __il, std::forward<_Args>(__args)...);
441 }
442
443 /**
444 * @brief Access the contained object.
445 *
446 * @tparam _ValueType A const-reference or CopyConstructible type.
447 * @param __any The object to access.
448 * @return The contained object.
449 * @throw bad_any_cast If <code>
450 * __any.type() != typeid(remove_reference_t<_ValueType>)
451 * </code>
452 */
453 template<typename _ValueType>
454 inline _ValueType any_cast(const any& __any)
455 {
456 using _Up = __remove_cvref_t<_ValueType>;
457 static_assert(any::__is_valid_cast<_ValueType>(),
458 "Template argument must be a reference or CopyConstructible type");
459 static_assert(is_constructible_v<_ValueType, const _Up&>,
460 "Template argument must be constructible from a const value.");
461 auto __p = any_cast<_Up>(&__any);
462 if (__p)
463 return static_cast<_ValueType>(*__p);
464 __throw_bad_any_cast();
465 }
466
467 /**
468 * @brief Access the contained object.
469 *
470 * @tparam _ValueType A reference or CopyConstructible type.
471 * @param __any The object to access.
472 * @return The contained object.
473 * @throw bad_any_cast If <code>
474 * __any.type() != typeid(remove_reference_t<_ValueType>)
475 * </code>
476 *
477 * @{
478 */
479 template<typename _ValueType>
480 inline _ValueType any_cast(any& __any)
481 {
482 using _Up = __remove_cvref_t<_ValueType>;
483 static_assert(any::__is_valid_cast<_ValueType>(),
484 "Template argument must be a reference or CopyConstructible type");
485 static_assert(is_constructible_v<_ValueType, _Up&>,
486 "Template argument must be constructible from an lvalue.");
487 auto __p = any_cast<_Up>(&__any);
488 if (__p)
489 return static_cast<_ValueType>(*__p);
490 __throw_bad_any_cast();
491 }
492
493 template<typename _ValueType>
494 inline _ValueType any_cast(any&& __any)
495 {
496 using _Up = __remove_cvref_t<_ValueType>;
497 static_assert(any::__is_valid_cast<_ValueType>(),
498 "Template argument must be a reference or CopyConstructible type");
499 static_assert(is_constructible_v<_ValueType, _Up>,
500 "Template argument must be constructible from an rvalue.");
501 auto __p = any_cast<_Up>(&__any);
502 if (__p)
503 return static_cast<_ValueType>(std::move(*__p));
504 __throw_bad_any_cast();
505 }
506 /// @}
507
508 /// @cond undocumented
509 template<typename _Tp>
510 void* __any_caster(const any* __any)
511 {
512 // any_cast<T> returns non-null if __any->type() == typeid(T) and
513 // typeid(T) ignores cv-qualifiers so remove them:
514 using _Up = remove_cv_t<_Tp>;
515 // The contained value has a decayed type, so if decay_t<U> is not U,
516 // then it's not possible to have a contained value of type U:
517 if constexpr (!is_same_v<decay_t<_Up>, _Up>)
518 return nullptr;
519 // Only copy constructible types can be used for contained values:
520 else if constexpr (!is_copy_constructible_v<_Up>)
521 return nullptr;
522 // First try comparing function addresses, which works without RTTI
523 else if (__any->_M_manager == &any::_Manager<_Up>::_S_manage
524#if __cpp_rtti
525 || __any->type() == typeid(_Tp)
526#endif
527 )
528 {
529 return any::_Manager<_Up>::_S_access(__any->_M_storage);
530 }
531 return nullptr;
532 }
533 /// @endcond
534
535 /**
536 * @brief Access the contained object.
537 *
538 * @tparam _ValueType The type of the contained object.
539 * @param __any A pointer to the object to access.
540 * @return The address of the contained object if <code>
541 * __any != nullptr && __any.type() == typeid(_ValueType)
542 * </code>, otherwise a null pointer.
543 *
544 * @{
545 */
546 template<typename _ValueType>
547 inline const _ValueType* any_cast(const any* __any) noexcept
548 {
549 if constexpr (is_object_v<_ValueType>)
550 if (__any)
551 return static_cast<_ValueType*>(__any_caster<_ValueType>(__any));
552 return nullptr;
553 }
554
555 template<typename _ValueType>
556 inline _ValueType* any_cast(any* __any) noexcept
557 {
558 if constexpr (is_object_v<_ValueType>)
559 if (__any)
560 return static_cast<_ValueType*>(__any_caster<_ValueType>(__any));
561 return nullptr;
562 }
563 /// @}
564
565 template<typename _Tp>
566 void
567 any::_Manager_internal<_Tp>::
568 _S_manage(_Op __which, const any* __any, _Arg* __arg)
569 {
570 // The contained object is in _M_storage._M_buffer
571 auto __ptr = reinterpret_cast<const _Tp*>(&__any->_M_storage._M_buffer);
572 switch (__which)
573 {
574 case _Op_access:
575 __arg->_M_obj = const_cast<_Tp*>(__ptr);
576 break;
577 case _Op_get_type_info:
578#if __cpp_rtti
579 __arg->_M_typeinfo = &typeid(_Tp);
580#endif
581 break;
582 case _Op_clone:
583 ::new(&__arg->_M_any->_M_storage._M_buffer) _Tp(*__ptr);
584 __arg->_M_any->_M_manager = __any->_M_manager;
585 break;
586 case _Op_destroy:
587 __ptr->~_Tp();
588 break;
589 case _Op_xfer:
590 ::new(&__arg->_M_any->_M_storage._M_buffer) _Tp
591 (std::move(*const_cast<_Tp*>(__ptr)));
592 __ptr->~_Tp();
593 __arg->_M_any->_M_manager = __any->_M_manager;
594 const_cast<any*>(__any)->_M_manager = nullptr;
595 break;
596 }
597 }
598
599 template<typename _Tp>
600 void
601 any::_Manager_external<_Tp>::
602 _S_manage(_Op __which, const any* __any, _Arg* __arg)
603 {
604 // The contained object is *_M_storage._M_ptr
605 auto __ptr = static_cast<const _Tp*>(__any->_M_storage._M_ptr);
606 switch (__which)
607 {
608 case _Op_access:
609 __arg->_M_obj = const_cast<_Tp*>(__ptr);
610 break;
611 case _Op_get_type_info:
612#if __cpp_rtti
613 __arg->_M_typeinfo = &typeid(_Tp);
614#endif
615 break;
616 case _Op_clone:
617 __arg->_M_any->_M_storage._M_ptr = new _Tp(*__ptr);
618 __arg->_M_any->_M_manager = __any->_M_manager;
619 break;
620 case _Op_destroy:
621 delete __ptr;
622 break;
623 case _Op_xfer:
624 __arg->_M_any->_M_storage._M_ptr = __any->_M_storage._M_ptr;
625 __arg->_M_any->_M_manager = __any->_M_manager;
626 const_cast<any*>(__any)->_M_manager = nullptr;
627 break;
628 }
629 }
630
631 /// @}
632
633 namespace __detail::__variant
634 {
635 template<typename> struct _Never_valueless_alt; // see <variant>
636
637 // Provide the strong exception-safety guarantee when emplacing an
638 // any into a variant.
639 template<>
640 struct _Never_valueless_alt<std::any>
641 : std::true_type
642 { };
643 } // namespace __detail::__variant
644
645_GLIBCXX_END_NAMESPACE_VERSION
646} // namespace std
647
648#endif // C++17
649#endif // _GLIBCXX_ANY