std_function.h source code [include/c++/7/bits/std

1	// Implementation of std::function -- C++ --
2
3	// Copyright (C) 2004-2017 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/bits/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_STD_FUNCTION_H
31	#define _GLIBCXX_STD_FUNCTION_H 1
32
33	#pragma GCC system_header
34
35	#if __cplusplus < 201103L
36	# include <bits/c++0x_warning.h>
37	#else
38
39	#if __cpp_rtti
40	# include <typeinfo>
41	#endif
42	#include <bits/stl_function.h>
43	#include <bits/invoke.h>
44	#include <bits/refwrap.h>
45	#include <bits/functexcept.h>
46
47	namespace std _GLIBCXX_VISIBILITY(default)
48	{
49	_GLIBCXX_BEGIN_NAMESPACE_VERSION
50
51	/**
52	* Derives from @c unary_function or @c binary_function, or perhaps
53	* nothing, depending on the number of arguments provided. The
54	* primary template is the basis case, which derives nothing.
55	*/
56	template<typename _Res, typename... _ArgTypes>
57	struct _Maybe_unary_or_binary_function { };
58
59	/// Derives from @c unary_function, as appropriate.
60	template<typename _Res, typename _T1>
61	struct _Maybe_unary_or_binary_function<_Res, _T1>
62	: std::unary_function<_T1, _Res> { };
63
64	/// Derives from @c binary_function, as appropriate.
65	template<typename _Res, typename _T1, typename _T2>
66	struct _Maybe_unary_or_binary_function<_Res, _T1, _T2>
67	: std::binary_function<_T1, _T2, _Res> { };
68
69
70	/**
71	* @brief Exception class thrown when class template function's
72	* operator() is called with an empty target.
73	* @ingroup exceptions
74	*/
75	class bad_function_call : public std::exception
76	{
77	public:
78	virtual ~bad_function_call() noexcept;
79
80	const char* what() const noexcept;
81	};
82
83	/**
84	* Trait identifying "location-invariant" types, meaning that the
85	* address of the object (or any of its members) will not escape.
86	* Trivially copyable types are location-invariant and users can
87	* specialize this trait for other types.
88	*/
89	template<typename _Tp>
90	struct __is_location_invariant
91	: is_trivially_copyable<_Tp>::type
92	{ };
93
94	class _Undefined_class;
95
96	union _Nocopy_types
97	{
98	void* _M_object;
99	const void* _M_const_object;
100	void (*_M_function_pointer)();
101	void (_Undefined_class::*_M_member_pointer)();
102	};
103
104	union [[gnu::may_alias]] _Any_data
105	{
106	void* _M_access() { return &_M_pod_data[0]; }
107	const void* _M_access() const { return &_M_pod_data[0]; }
108
109	template<typename _Tp>
110	_Tp&
111	_M_access()
112	{ return static_cast<_Tp>(_M_access()); }
113
114	template<typename _Tp>
115	const _Tp&
116	_M_access() const
117	{ return static_cast<const _Tp>(_M_access()); }
118
119	_Nocopy_types _M_unused;
120	char _M_pod_data[sizeof(_Nocopy_types)];
121	};
122
123	enum _Manager_operation
124	{
125	__get_type_info,
126	__get_functor_ptr,
127	__clone_functor,
128	__destroy_functor
129	};
130
131	// Simple type wrapper that helps avoid annoying const problems
132	// when casting between void pointers and pointers-to-pointers.
133	template<typename _Tp>
134	struct _Simple_type_wrapper
135	{
136	_Simple_type_wrapper(_Tp __value) : __value(__value) { }
137
138	_Tp __value;
139	};
140
141	template<typename _Tp>
142	struct __is_location_invariant<_Simple_type_wrapper<_Tp> >
143	: __is_location_invariant<_Tp>
144	{ };
145
146	template<typename _Signature>
147	class function;
148
149	/// Base class of all polymorphic function object wrappers.
150	class _Function_base
151	{
152	public:
153	static const std::size_t _M_max_size = sizeof(_Nocopy_types);
154	static const std::size_t _M_max_align = __alignof__(_Nocopy_types);
155
156	template<typename _Functor>
157	class _Base_manager
158	{
159	protected:
160	static const bool __stored_locally =
161	(__is_location_invariant<_Functor>::value
162	&& sizeof(_Functor) <= _M_max_size
163	&& __alignof__(_Functor) <= _M_max_align
164	&& (_M_max_align % __alignof__(_Functor) == 0));
165
166	typedef integral_constant<bool, __stored_locally> _Local_storage;
167
168	// Retrieve a pointer to the function object
169	static _Functor*
170	_M_get_pointer(const _Any_data& __source)
171	{
172	const _Functor* __ptr =
173	__stored_locally? std::__addressof(__source._M_access<_Functor>())
174	/* have stored a pointer / : __source._M_access<_Functor>();
175	return const_cast<_Functor*>(__ptr);
176	}
177
178	// Clone a location-invariant function object that fits within
179	// an _Any_data structure.
180	static void
181	_M_clone(_Any_data& __dest, const _Any_data& __source, true_type)
182	{
183	::new (__dest._M_access()) _Functor(__source._M_access<_Functor>());
184	}
185
186	// Clone a function object that is not location-invariant or
187	// that cannot fit into an _Any_data structure.
188	static void
189	_M_clone(_Any_data& __dest, const _Any_data& __source, false_type)
190	{
191	__dest._M_access<_Functor*>() =
192	new _Functor(__source._M_access<_Functor>());
193	}
194
195	// Destroying a location-invariant object may still require
196	// destruction.
197	static void
198	_M_destroy(_Any_data& __victim, true_type)
199	{
200	__victim._M_access<_Functor>().~_Functor();
201	}
202
203	// Destroying an object located on the heap.
204	static void
205	_M_destroy(_Any_data& __victim, false_type)
206	{
207	delete __victim._M_access<_Functor*>();
208	}
209
210	public:
211	static bool
212	_M_manager(_Any_data& __dest, const _Any_data& __source,
213	_Manager_operation __op)
214	{
215	switch (__op)
216	{
217	#if __cpp_rtti
218	case __get_type_info:
219	__dest._M_access<const type_info*>() = &typeid(_Functor);
220	break;
221	#endif
222	case __get_functor_ptr:
223	__dest._M_access<_Functor*>() = _M_get_pointer(__source);
224	break;
225
226	case __clone_functor:
227	_M_clone(__dest, __source, _Local_storage());
228	break;
229
230	case __destroy_functor:
231	_M_destroy(__dest, _Local_storage());
232	break;
233	}
234	return false;
235	}
236
237	static void
238	_M_init_functor(_Any_data& __functor, _Functor&& __f)
239	{ _M_init_functor(__functor, std::move(__f), _Local_storage()); }
240
241	template<typename _Signature>
242	static bool
243	_M_not_empty_function(const function<_Signature>& __f)
244	{ return static_cast<bool>(__f); }
245
246	template<typename _Tp>
247	static bool
248	_M_not_empty_function(_Tp* __fp)
249	{ return __fp != nullptr; }
250
251	template<typename _Class, typename _Tp>
252	static bool
253	_M_not_empty_function(_Tp _Class::* __mp)
254	{ return __mp != nullptr; }
255
256	template<typename _Tp>
257	static bool
258	_M_not_empty_function(const _Tp&)
259	{ return true; }
260
261	private:
262	static void
263	_M_init_functor(_Any_data& __functor, _Functor&& __f, true_type)
264	{ ::new (__functor._M_access()) _Functor(std::move(__f)); }
265
266	static void
267	_M_init_functor(_Any_data& __functor, _Functor&& __f, false_type)
268	{ __functor._M_access<_Functor*>() = new _Functor(std::move(__f)); }
269	};
270
271	_Function_base() : _M_manager(nullptr) { }
272
273	~_Function_base()
274	{
275	if (_M_manager)
276	_M_manager(_M_functor, _M_functor, __destroy_functor);
277	}
278
279	bool _M_empty() const { return !_M_manager; }
280
281	typedef bool (*_Manager_type)(_Any_data&, const _Any_data&,
282	_Manager_operation);
283
284	_Any_data _M_functor;
285	_Manager_type _M_manager;
286	};
287
288	template<typename _Signature, typename _Functor>
289	class _Function_handler;
290
291	template<typename _Res, typename _Functor, typename... _ArgTypes>
292	class _Function_handler<_Res(_ArgTypes...), _Functor>
293	: public _Function_base::_Base_manager<_Functor>
294	{
295	typedef _Function_base::_Base_manager<_Functor> _Base;
296
297	public:
298	static _Res
299	_M_invoke(const _Any_data& __functor, _ArgTypes&&... __args)
300	{
301	return (*_Base::_M_get_pointer(__functor))(
302	std::forward<_ArgTypes>(__args)...);
303	}
304	};
305
306	template<typename _Functor, typename... _ArgTypes>
307	class _Function_handler<void(_ArgTypes...), _Functor>
308	: public _Function_base::_Base_manager<_Functor>
309	{
310	typedef _Function_base::_Base_manager<_Functor> _Base;
311
312	public:
313	static void
314	_M_invoke(const _Any_data& __functor, _ArgTypes&&... __args)
315	{
316	(*_Base::_M_get_pointer(__functor))(
317	std::forward<_ArgTypes>(__args)...);
318	}
319	};
320
321	template<typename _Class, typename _Member, typename _Res,
322	typename... _ArgTypes>
323	class _Function_handler<_Res(_ArgTypes...), _Member _Class::*>
324	: public _Function_handler<void(_ArgTypes...), _Member _Class::*>
325	{
326	typedef _Function_handler<void(_ArgTypes...), _Member _Class::*>
327	_Base;
328
329	public:
330	static _Res
331	_M_invoke(const _Any_data& __functor, _ArgTypes&&... __args)
332	{
333	return std::__invoke(_Base::_M_get_pointer(__functor)->__value,
334	std::forward<_ArgTypes>(__args)...);
335	}
336	};
337
338	template<typename _Class, typename _Member, typename... _ArgTypes>
339	class _Function_handler<void(_ArgTypes...), _Member _Class::*>
340	: public _Function_base::_Base_manager<
341	_Simple_type_wrapper< _Member _Class::* > >
342	{
343	typedef _Member _Class::* _Functor;
344	typedef _Simple_type_wrapper<_Functor> _Wrapper;
345	typedef _Function_base::_Base_manager<_Wrapper> _Base;
346
347	public:
348	static bool
349	_M_manager(_Any_data& __dest, const _Any_data& __source,
350	_Manager_operation __op)
351	{
352	switch (__op)
353	{
354	#if __cpp_rtti
355	case __get_type_info:
356	__dest._M_access<const type_info*>() = &typeid(_Functor);
357	break;
358	#endif
359	case __get_functor_ptr:
360	__dest._M_access<_Functor*>() =
361	&_Base::_M_get_pointer(__source)->__value;
362	break;
363
364	default:
365	_Base::_M_manager(__dest, __source, __op);
366	}
367	return false;
368	}
369
370	static void
371	_M_invoke(const _Any_data& __functor, _ArgTypes&&... __args)
372	{
373	std::__invoke(_Base::_M_get_pointer(__functor)->__value,
374	std::forward<_ArgTypes>(__args)...);
375	}
376	};
377
378	template<typename _From, typename _To>
379	using __check_func_return_type
380	= __or_<is_void<_To>, is_same<_From, _To>, is_convertible<_From, _To>>;
381
382	/**
383	* @brief Primary class template for std::function.
384	* @ingroup functors
385	*
386	* Polymorphic function wrapper.
387	*/
388	template<typename _Res, typename... _ArgTypes>
389	class function<_Res(_ArgTypes...)>
390	: public _Maybe_unary_or_binary_function<_Res, _ArgTypes...>,
391	private _Function_base
392	{
393	template<typename _Func,
394	typename _Res2 = typename result_of<_Func&(_ArgTypes...)>::type>
395	struct _Callable : __check_func_return_type<_Res2, _Res> { };
396
397	// Used so the return type convertibility checks aren't done when
398	// performing overload resolution for copy construction/assignment.
399	template<typename _Tp>
400	struct _Callable<function, _Tp> : false_type { };
401
402	template<typename _Cond, typename _Tp>
403	using _Requires = typename enable_if<_Cond::value, _Tp>::type;
404
405	public:
406	typedef _Res result_type;
407
408	// [3.7.2.1] construct/copy/destroy
409
410	/**
411	* @brief Default construct creates an empty function call wrapper.
412	* @post @c !(bool)*this
413	*/
414	function() noexcept
415	: _Function_base() { }
416
417	/**
418	* @brief Creates an empty function call wrapper.
419	* @post @c !(bool)*this
420	*/
421	function(nullptr_t) noexcept
422	: _Function_base() { }
423
424	/**
425	* @brief %Function copy constructor.
426	* @param __x A %function object with identical call signature.
427	* @post @c bool(*this) == bool(__x)
428	*
429	* The newly-created %function contains a copy of the target of @a
430	* __x (if it has one).
431	*/
432	function(const function& __x);
433
434	/**
435	* @brief %Function move constructor.
436	* @param __x A %function object rvalue with identical call signature.
437	*
438	* The newly-created %function contains the target of @a __x
439	* (if it has one).
440	*/
441	function(function&& __x) noexcept : _Function_base()
442	{
443	__x.swap(*this);
444	}
445
446	/**
447	* @brief Builds a %function that targets a copy of the incoming
448	* function object.
449	* @param __f A %function object that is callable with parameters of
450	* type @c T1, @c T2, ..., @c TN and returns a value convertible
451	* to @c Res.
452	*
453	* The newly-created %function object will target a copy of
454	* @a __f. If @a __f is @c reference_wrapper<F>, then this function
455	* object will contain a reference to the function object @c
456	* __f.get(). If @a __f is a NULL function pointer or NULL
457	* pointer-to-member, the newly-created object will be empty.
458	*
459	* If @a __f is a non-NULL function pointer or an object of type @c
460	* reference_wrapper<F>, this function will not throw.
461	*/
462	template<typename _Functor,
463	typename = _Requires<__not_<is_same<_Functor, function>>, void>,
464	typename = _Requires<_Callable<_Functor>, void>>
465	function(_Functor);
466
467	/**
468	* @brief %Function assignment operator.
469	* @param __x A %function with identical call signature.
470	* @post @c (bool)*this == (bool)x
471	* @returns @c *this
472	*
473	* The target of @a __x is copied to @c *this. If @a __x has no
474	* target, then @c *this will be empty.
475	*
476	* If @a __x targets a function pointer or a reference to a function
477	* object, then this operation will not throw an %exception.
478	*/
479	function&
480	operator=(const function& __x)
481	{
482	function(__x).swap(*this);
483	return *this;
484	}
485
486	/**
487	* @brief %Function move-assignment operator.
488	* @param __x A %function rvalue with identical call signature.
489	* @returns @c *this
490	*
491	* The target of @a __x is moved to @c *this. If @a __x has no
492	* target, then @c *this will be empty.
493	*
494	* If @a __x targets a function pointer or a reference to a function
495	* object, then this operation will not throw an %exception.
496	*/
497	function&
498	operator=(function&& __x) noexcept
499	{
500	function(std::move(__x)).swap(*this);
501	return *this;
502	}
503
504	/**
505	* @brief %Function assignment to zero.
506	* @post @c !(bool)*this
507	* @returns @c *this
508	*
509	* The target of @c *this is deallocated, leaving it empty.
510	*/
511	function&
512	operator=(nullptr_t) noexcept
513	{
514	if (_M_manager)
515	{
516	_M_manager(_M_functor, _M_functor, __destroy_functor);
517	_M_manager = nullptr;
518	_M_invoker = nullptr;
519	}
520	return *this;
521	}
522
523	/**
524	* @brief %Function assignment to a new target.
525	* @param __f A %function object that is callable with parameters of
526	* type @c T1, @c T2, ..., @c TN and returns a value convertible
527	* to @c Res.
528	* @return @c *this
529	*
530	* This %function object wrapper will target a copy of @a
531	* __f. If @a __f is @c reference_wrapper<F>, then this function
532	* object will contain a reference to the function object @c
533	* __f.get(). If @a __f is a NULL function pointer or NULL
534	* pointer-to-member, @c this object will be empty.
535	*
536	* If @a __f is a non-NULL function pointer or an object of type @c
537	* reference_wrapper<F>, this function will not throw.
538	*/
539	template<typename _Functor>
540	_Requires<_Callable<typename decay<_Functor>::type>, function&>
541	operator=(_Functor&& __f)
542	{
543	function(std::forward<_Functor>(__f)).swap(*this);
544	return *this;
545	}
546
547	/// @overload
548	template<typename _Functor>
549	function&
550	operator=(reference_wrapper<_Functor> __f) noexcept
551	{
552	function(__f).swap(*this);
553	return *this;
554	}
555
556	// [3.7.2.2] function modifiers
557
558	/**
559	* @brief Swap the targets of two %function objects.
560	* @param __x A %function with identical call signature.
561	*
562	* Swap the targets of @c this function object and @a __f. This
563	* function will not throw an %exception.
564	*/
565	void swap(function& __x) noexcept
566	{
567	std::swap(_M_functor, __x._M_functor);
568	std::swap(_M_manager, __x._M_manager);
569	std::swap(_M_invoker, __x._M_invoker);
570	}
571
572	// [3.7.2.3] function capacity
573
574	/**
575	* @brief Determine if the %function wrapper has a target.
576	*
577	* @return @c true when this %function object contains a target,
578	* or @c false when it is empty.
579	*
580	* This function will not throw an %exception.
581	*/
582	explicit operator bool() const noexcept
583	{ return !_M_empty(); }
584
585	// [3.7.2.4] function invocation
586
587	/**
588	* @brief Invokes the function targeted by @c *this.
589	* @returns the result of the target.
590	* @throws bad_function_call when @c !(bool)*this
591	*
592	* The function call operator invokes the target function object
593	* stored by @c this.
594	*/
595	_Res operator()(_ArgTypes... __args) const;
596
597	#if __cpp_rtti
598	// [3.7.2.5] function target access
599	/**
600	* @brief Determine the type of the target of this function object
601	* wrapper.
602	*
603	* @returns the type identifier of the target function object, or
604	* @c typeid(void) if @c !(bool)*this.
605	*
606	* This function will not throw an %exception.
607	*/
608	const type_info& target_type() const noexcept;
609
610	/**
611	* @brief Access the stored target function object.
612	*
613	* @return Returns a pointer to the stored target function object,
614	* if @c typeid(_Functor).equals(target_type()); otherwise, a NULL
615	* pointer.
616	*
617	* This function does not throw exceptions.
618	*
619	* @{
620	*/
621	template<typename _Functor> _Functor* target() noexcept;
622
623	template<typename _Functor> const _Functor* target() const noexcept;
624	// @}
625	#endif
626
627	private:
628	using _Invoker_type = _Res (*)(const _Any_data&, _ArgTypes&&...);
629	_Invoker_type _M_invoker;
630	};
631
632	#if __cpp_deduction_guides >= 201606
633	template<typename>
634	struct __function_guide_helper
635	{ };
636
637	template<typename _Res, typename _Tp, bool _Nx, typename... _Args>
638	struct __function_guide_helper<
639	_Res (_Tp::*) (_Args...) noexcept(_Nx)
640	>
641	{ using type = _Res(_Args...); };
642
643	template<typename _Res, typename _Tp, bool _Nx, typename... _Args>
644	struct __function_guide_helper<
645	_Res (_Tp::*) (_Args...) & noexcept(_Nx)
646	>
647	{ using type = _Res(_Args...); };
648
649	template<typename _Res, typename _Tp, bool _Nx, typename... _Args>
650	struct __function_guide_helper<
651	_Res (_Tp::*) (_Args...) const noexcept(_Nx)
652	>
653	{ using type = _Res(_Args...); };
654
655	template<typename _Res, typename _Tp, bool _Nx, typename... _Args>
656	struct __function_guide_helper<
657	_Res (_Tp::*) (_Args...) const & noexcept(_Nx)
658	>
659	{ using type = _Res(_Args...); };
660
661	template<typename _Res, typename... _ArgTypes>
662	function(_Res(*)(_ArgTypes...)) -> function<_Res(_ArgTypes...)>;
663
664	template<typename _Functor, typename _Signature = typename
665	__function_guide_helper<decltype(&_Functor::operator())>::type>
666	function(_Functor) -> function<_Signature>;
667	#endif
668
669	// Out-of-line member definitions.
670	template<typename _Res, typename... _ArgTypes>
671	function<_Res(_ArgTypes...)>::
672	function(const function& __x)
673	: _Function_base()
674	{
675	if (static_cast<bool>(__x))
676	{
677	__x._M_manager(_M_functor, __x._M_functor, __clone_functor);
678	_M_invoker = __x._M_invoker;
679	_M_manager = __x._M_manager;
680	}
681	}
682
683	template<typename _Res, typename... _ArgTypes>
684	template<typename _Functor, typename, typename>
685	function<_Res(_ArgTypes...)>::
686	function(_Functor __f)
687	: _Function_base()
688	{
689	typedef _Function_handler<_Res(_ArgTypes...), _Functor> _My_handler;
690
691	if (_My_handler::_M_not_empty_function(__f))
692	{
693	_My_handler::_M_init_functor(_M_functor, std::move(__f));
694	_M_invoker = &_My_handler::_M_invoke;
695	_M_manager = &_My_handler::_M_manager;
696	}
697	}
698
699	template<typename _Res, typename... _ArgTypes>
700	_Res
701	function<_Res(_ArgTypes...)>::
702	operator()(_ArgTypes... __args) const
703	{
704	if (_M_empty())
705	__throw_bad_function_call();
706	return _M_invoker(_M_functor, std::forward<_ArgTypes>(__args)...);
707	}
708
709	#if __cpp_rtti
710	template<typename _Res, typename... _ArgTypes>
711	const type_info&
712	function<_Res(_ArgTypes...)>::
713	target_type() const noexcept
714	{
715	if (_M_manager)
716	{
717	_Any_data __typeinfo_result;
718	_M_manager(__typeinfo_result, _M_functor, __get_type_info);
719	return __typeinfo_result._M_access<const type_info>();
720	}
721	else
722	return typeid(void);
723	}
724
725	template<typename _Res, typename... _ArgTypes>
726	template<typename _Functor>
727	_Functor*
728	function<_Res(_ArgTypes...)>::
729	target() noexcept
730	{
731	const function* __const_this = this;
732	const _Functor* __func = __const_this->template target<_Functor>();
733	return const_cast<_Functor*>(__func);
734	}
735
736	template<typename _Res, typename... _ArgTypes>
737	template<typename _Functor>
738	const _Functor*
739	function<_Res(_ArgTypes...)>::
740	target() const noexcept
741	{
742	if (typeid(_Functor) == target_type() && _M_manager)
743	{
744	_Any_data __ptr;
745	_M_manager(__ptr, _M_functor, __get_functor_ptr);
746	return __ptr._M_access<const _Functor*>();
747	}
748	else
749	return nullptr;
750	}
751	#endif
752
753	// [20.7.15.2.6] null pointer comparisons
754
755	/**
756	* @brief Compares a polymorphic function object wrapper against 0
757	* (the NULL pointer).
758	* @returns @c true if the wrapper has no target, @c false otherwise
759	*
760	* This function will not throw an %exception.
761	*/
762	template<typename _Res, typename... _Args>
763	inline bool
764	operator==(const function<_Res(_Args...)>& __f, nullptr_t) noexcept
765	{ return !static_cast<bool>(__f); }
766
767	/// @overload
768	template<typename _Res, typename... _Args>
769	inline bool
770	operator==(nullptr_t, const function<_Res(_Args...)>& __f) noexcept
771	{ return !static_cast<bool>(__f); }
772
773	/**
774	* @brief Compares a polymorphic function object wrapper against 0
775	* (the NULL pointer).
776	* @returns @c false if the wrapper has no target, @c true otherwise
777	*
778	* This function will not throw an %exception.
779	*/
780	template<typename _Res, typename... _Args>
781	inline bool
782	operator!=(const function<_Res(_Args...)>& __f, nullptr_t) noexcept
783	{ return static_cast<bool>(__f); }
784
785	/// @overload
786	template<typename _Res, typename... _Args>
787	inline bool
788	operator!=(nullptr_t, const function<_Res(_Args...)>& __f) noexcept
789	{ return static_cast<bool>(__f); }
790
791
792	// [20.7.15.2.7] specialized algorithms
793
794	/**
795	* @brief Swap the targets of two polymorphic function object wrappers.
796	*
797	* This function will not throw an %exception.
798	*/
799	// _GLIBCXX_RESOLVE_LIB_DEFECTS
800	// 2062. Effect contradictions w/o no-throw guarantee of std::function swaps
801	template<typename _Res, typename... _Args>
802	inline void
803	swap(function<_Res(_Args...)>& __x, function<_Res(_Args...)>& __y) noexcept
804	{ __x.swap(__y); }
805
806	_GLIBCXX_END_NAMESPACE_VERSION
807	} // namespace std
808
809	#endif // C++11
810
811	#endif // _GLIBCXX_STD_FUNCTION_H
812