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The C and C++ Include Header Files
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1 // Implementation of std::function -*- C++ -*- 2 3 // Copyright (C) 2004-2025 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/std_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 #ifdef _GLIBCXX_SYSHDR 34 #pragma GCC system_header 35 #endif 36 37 #if __cplusplus < 201103L 38 # include <bits/c++0x_warning.h> 39 #else 40 41 #include <new> // placement new 42 #include <typeinfo> // typeid 43 #include <bits/invoke.h> // __invoke_r 44 #include <bits/refwrap.h> // ref wrapper, _Maybe_unary_or_binary_function 45 #include <bits/functexcept.h> // __throw_bad_function_call 46 47 namespace std _GLIBCXX_VISIBILITY(default) 48 { 49 _GLIBCXX_BEGIN_NAMESPACE_VERSION 50 51 /** 52 * @brief Exception class thrown when class template function's 53 * operator() is called with an empty target. 54 * @ingroup exceptions 55 */ 56 class bad_function_call : public std::exception 57 { 58 public: 59 virtual ~bad_function_call() noexcept; 60 61 const char* what() const noexcept; 62 }; 63 64 /** 65 * Trait identifying "location-invariant" types, meaning that the 66 * address of the object (or any of its members) will not escape. 67 * Trivially copyable types are location-invariant and users can 68 * specialize this trait for other types. 69 */ 70 template<typename _Tp> 71 struct __is_location_invariant 72 : is_trivially_copyable<_Tp>::type 73 { }; 74 75 class _Undefined_class; 76 77 union _Nocopy_types 78 { 79 void* _M_object; 80 const void* _M_const_object; 81 void (*_M_function_pointer)(); 82 void (_Undefined_class::*_M_member_pointer)(); 83 }; 84 85 union [[gnu::may_alias]] _Any_data 86 { 87 void* _M_access() noexcept { return &_M_pod_data[0]; } 88 const void* _M_access() const noexcept { return &_M_pod_data[0]; } 89 90 template<typename _Tp> 91 _Tp& 92 _M_access() noexcept 93 { return *static_cast<_Tp*>(_M_access()); } 94 95 template<typename _Tp> 96 const _Tp& 97 _M_access() const noexcept 98 { return *static_cast<const _Tp*>(_M_access()); } 99 100 _Nocopy_types _M_unused; 101 char _M_pod_data[sizeof(_Nocopy_types)]; 102 }; 103 104 enum _Manager_operation 105 { 106 __get_type_info, 107 __get_functor_ptr, 108 __clone_functor, 109 __destroy_functor 110 }; 111 112 template<typename _Signature> 113 class function; 114 115 /// Base class of all polymorphic function object wrappers. 116 class _Function_base 117 { 118 public: 119 static const size_t _M_max_size = sizeof(_Nocopy_types); 120 static const size_t _M_max_align = __alignof__(_Nocopy_types); 121 122 template<typename _Functor> 123 class _Base_manager 124 { 125 protected: 126 static const bool __stored_locally = 127 (__is_location_invariant<_Functor>::value 128 && sizeof(_Functor) <= _M_max_size 129 && __alignof__(_Functor) <= _M_max_align 130 && (_M_max_align % __alignof__(_Functor) == 0)); 131 132 using _Local_storage = integral_constant<bool, __stored_locally>; 133 134 // Retrieve a pointer to the function object 135 static _Functor* 136 _M_get_pointer(const _Any_data& __source) noexcept 137 { 138 if _GLIBCXX17_CONSTEXPR (__stored_locally) 139 { 140 const _Functor& __f = __source._M_access<_Functor>(); 141 return const_cast<_Functor*>(std::__addressof(__f)); 142 } 143 else // have stored a pointer 144 return __source._M_access<_Functor*>(); 145 } 146 147 private: 148 // Construct a location-invariant function object that fits within 149 // an _Any_data structure. 150 template<typename _Fn> 151 static void 152 _M_create(_Any_data& __dest, _Fn&& __f, true_type) 153 { 154 ::new (__dest._M_access()) _Functor(std::forward<_Fn>(__f)); 155 } 156 157 // Construct a function object on the heap and store a pointer. 158 template<typename _Fn> 159 static void 160 _M_create(_Any_data& __dest, _Fn&& __f, false_type) 161 { 162 __dest._M_access<_Functor*>() 163 = new _Functor(std::forward<_Fn>(__f)); 164 } 165 166 // Destroy an object stored in the internal buffer. 167 static void 168 _M_destroy(_Any_data& __victim, true_type) 169 { 170 __victim._M_access<_Functor>().~_Functor(); 171 } 172 173 // Destroy an object located on the heap. 174 static void 175 _M_destroy(_Any_data& __victim, false_type) 176 { 177 delete __victim._M_access<_Functor*>(); 178 } 179 180 public: 181 static bool 182 _M_manager(_Any_data& __dest, const _Any_data& __source, 183 _Manager_operation __op) 184 { 185 switch (__op) 186 { 187 case __get_type_info: 188 #if __cpp_rtti 189 __dest._M_access<const type_info*>() = &typeid(_Functor); 190 #else 191 __dest._M_access<const type_info*>() = nullptr; 192 #endif 193 break; 194 195 case __get_functor_ptr: 196 __dest._M_access<_Functor*>() = _M_get_pointer(__source); 197 break; 198 199 case __clone_functor: 200 _M_init_functor(__dest, 201 *const_cast<const _Functor*>(_M_get_pointer(__source))); 202 break; 203 204 case __destroy_functor: 205 _M_destroy(__dest, _Local_storage()); 206 break; 207 } 208 return false; 209 } 210 211 template<typename _Fn> 212 static void 213 _M_init_functor(_Any_data& __functor, _Fn&& __f) 214 noexcept(__and_<_Local_storage, 215 is_nothrow_constructible<_Functor, _Fn>>::value) 216 { 217 _M_create(__functor, std::forward<_Fn>(__f), _Local_storage()); 218 } 219 220 template<typename _Signature> 221 static bool 222 _M_not_empty_function(const function<_Signature>& __f) noexcept 223 { return static_cast<bool>(__f); } 224 225 template<typename _Tp> 226 static bool 227 _M_not_empty_function(_Tp* __fp) noexcept 228 { return __fp != nullptr; } 229 230 template<typename _Class, typename _Tp> 231 static bool 232 _M_not_empty_function(_Tp _Class::* __mp) noexcept 233 { return __mp != nullptr; } 234 235 template<typename _Tp> 236 static bool 237 _M_not_empty_function(const _Tp&) noexcept 238 { return true; } 239 }; 240 241 _Function_base() = default; 242 243 ~_Function_base() 244 { 245 if (_M_manager) 246 _M_manager(_M_functor, _M_functor, __destroy_functor); 247 } 248 249 bool _M_empty() const { return !_M_manager; } 250 251 using _Manager_type 252 = bool (*)(_Any_data&, const _Any_data&, _Manager_operation); 253 254 _Any_data _M_functor{}; 255 _Manager_type _M_manager{}; 256 }; 257 258 template<typename _Signature, typename _Functor> 259 class _Function_handler; 260 261 template<typename _Res, typename _Functor, typename... _ArgTypes> 262 class _Function_handler<_Res(_ArgTypes...), _Functor> 263 : public _Function_base::_Base_manager<_Functor> 264 { 265 using _Base = _Function_base::_Base_manager<_Functor>; 266 267 public: 268 static bool 269 _M_manager(_Any_data& __dest, const _Any_data& __source, 270 _Manager_operation __op) 271 { 272 switch (__op) 273 { 274 #if __cpp_rtti 275 case __get_type_info: 276 __dest._M_access<const type_info*>() = &typeid(_Functor); 277 break; 278 #endif 279 case __get_functor_ptr: 280 __dest._M_access<_Functor*>() = _Base::_M_get_pointer(__source); 281 break; 282 283 default: 284 _Base::_M_manager(__dest, __source, __op); 285 } 286 return false; 287 } 288 289 static _Res 290 _M_invoke(const _Any_data& __functor, _ArgTypes&&... __args) 291 { 292 return std::__invoke_r<_Res>(*_Base::_M_get_pointer(__functor), 293 std::forward<_ArgTypes>(__args)...); 294 } 295 296 template<typename _Fn> 297 static constexpr bool 298 _S_nothrow_init() noexcept 299 { 300 return __and_<typename _Base::_Local_storage, 301 is_nothrow_constructible<_Functor, _Fn>>::value; 302 } 303 }; 304 305 // Specialization for invalid types 306 template<> 307 class _Function_handler<void, void> 308 { 309 public: 310 static bool 311 _M_manager(_Any_data&, const _Any_data&, _Manager_operation) 312 { return false; } 313 }; 314 315 // Avoids instantiating ill-formed specializations of _Function_handler 316 // in std::function<_Signature>::target<_Functor>(). 317 // e.g. _Function_handler<Sig, void()> and _Function_handler<Sig, void> 318 // would be ill-formed. 319 template<typename _Signature, typename _Functor, 320 bool __valid = is_object<_Functor>::value> 321 struct _Target_handler 322 : _Function_handler<_Signature, typename remove_cv<_Functor>::type> 323 { }; 324 325 template<typename _Signature, typename _Functor> 326 struct _Target_handler<_Signature, _Functor, false> 327 : _Function_handler<void, void> 328 { }; 329 330 /** 331 * @brief Polymorphic function wrapper. 332 * @ingroup functors 333 * @since C++11 334 */ 335 template<typename _Res, typename... _ArgTypes> 336 class function<_Res(_ArgTypes...)> 337 : public _Maybe_unary_or_binary_function<_Res, _ArgTypes...>, 338 private _Function_base 339 { 340 // Equivalent to std::decay_t except that it produces an invalid type 341 // if the decayed type is the current specialization of std::function. 342 template<typename _Func, 343 bool _Self = is_same<__remove_cvref_t<_Func>, function>::value> 344 using _Decay_t 345 = typename __enable_if_t<!_Self, decay<_Func>>::type; 346 347 template<typename _Func, 348 typename _DFunc = _Decay_t<_Func>, 349 typename _Res2 = __invoke_result<_DFunc&, _ArgTypes...>> 350 struct _Callable 351 : __is_invocable_impl<_Res2, _Res>::type 352 { }; 353 354 template<typename _Cond, typename _Tp = void> 355 using _Requires = __enable_if_t<_Cond::value, _Tp>; 356 357 template<typename _Functor> 358 using _Handler 359 = _Function_handler<_Res(_ArgTypes...), __decay_t<_Functor>>; 360 361 public: 362 typedef _Res result_type; 363 364 // [3.7.2.1] construct/copy/destroy 365 366 /** 367 * @brief Default construct creates an empty function call wrapper. 368 * @post `!(bool)*this` 369 */ 370 function() noexcept 371 : _Function_base() { } 372 373 /** 374 * @brief Creates an empty function call wrapper. 375 * @post @c !(bool)*this 376 */ 377 function(nullptr_t) noexcept 378 : _Function_base() { } 379 380 /** 381 * @brief %Function copy constructor. 382 * @param __x A %function object with identical call signature. 383 * @post `bool(*this) == bool(__x)` 384 * 385 * The newly-created %function contains a copy of the target of 386 * `__x` (if it has one). 387 */ 388 function(const function& __x) 389 : _Function_base() 390 { 391 if (static_cast<bool>(__x)) 392 { 393 __x._M_manager(_M_functor, __x._M_functor, __clone_functor); 394 _M_invoker = __x._M_invoker; 395 _M_manager = __x._M_manager; 396 } 397 } 398 399 /** 400 * @brief %Function move constructor. 401 * @param __x A %function object rvalue with identical call signature. 402 * 403 * The newly-created %function contains the target of `__x` 404 * (if it has one). 405 */ 406 function(function&& __x) noexcept 407 : _Function_base(), _M_invoker(__x._M_invoker) 408 { 409 if (static_cast<bool>(__x)) 410 { 411 _M_functor = __x._M_functor; 412 _M_manager = __x._M_manager; 413 __x._M_manager = nullptr; 414 __x._M_invoker = nullptr; 415 } 416 } 417 418 /** 419 * @brief Builds a %function that targets a copy of the incoming 420 * function object. 421 * @param __f A %function object that is callable with parameters of 422 * type `ArgTypes...` and returns a value convertible to `Res`. 423 * 424 * The newly-created %function object will target a copy of 425 * `__f`. If `__f` is `reference_wrapper<F>`, then this function 426 * object will contain a reference to the function object `__f.get()`. 427 * If `__f` is a null function pointer, null pointer-to-member, or 428 * empty `std::function`, the newly-created object will be empty. 429 * 430 * If `__f` is a non-null function pointer or an object of type 431 * `reference_wrapper<F>`, this function will not throw. 432 */ 433 // _GLIBCXX_RESOLVE_LIB_DEFECTS 434 // 2774. std::function construction vs assignment 435 template<typename _Functor, 436 typename _Constraints = _Requires<_Callable<_Functor>>> 437 function(_Functor&& __f) 438 noexcept(_Handler<_Functor>::template _S_nothrow_init<_Functor>()) 439 : _Function_base() 440 { 441 static_assert(is_copy_constructible<__decay_t<_Functor>>::value, 442 "std::function target must be copy-constructible"); 443 static_assert(is_constructible<__decay_t<_Functor>, _Functor>::value, 444 "std::function target must be constructible from the " 445 "constructor argument"); 446 447 using _My_handler = _Handler<_Functor>; 448 449 if (_My_handler::_M_not_empty_function(__f)) 450 { 451 _My_handler::_M_init_functor(_M_functor, 452 std::forward<_Functor>(__f)); 453 _M_invoker = &_My_handler::_M_invoke; 454 _M_manager = &_My_handler::_M_manager; 455 } 456 } 457 458 /** 459 * @brief Function assignment operator. 460 * @param __x A %function with identical call signature. 461 * @post `(bool)*this == (bool)x` 462 * @returns `*this` 463 * 464 * The target of `__x` is copied to `*this`. If `__x` has no 465 * target, then `*this` will be empty. 466 * 467 * If `__x` targets a function pointer or a reference to a function 468 * object, then this operation will not throw an exception. 469 */ 470 function& 471 operator=(const function& __x) 472 { 473 function(__x).swap(*this); 474 return *this; 475 } 476 477 /** 478 * @brief Function move-assignment operator. 479 * @param __x A %function rvalue with identical call signature. 480 * @returns `*this` 481 * 482 * The target of `__x` is moved to `*this`. If `__x` has no 483 * target, then `*this` will be empty. 484 * 485 * If `__x` targets a function pointer or a reference to a function 486 * object, then this operation will not throw an exception. 487 */ 488 function& 489 operator=(function&& __x) noexcept 490 { 491 function(std::move(__x)).swap(*this); 492 return *this; 493 } 494 495 /** 496 * @brief Function assignment to empty. 497 * @post `!(bool)*this` 498 * @returns `*this` 499 * 500 * The target of `*this` is deallocated, leaving it empty. 501 */ 502 function& 503 operator=(nullptr_t) noexcept 504 { 505 if (_M_manager) 506 { 507 _M_manager(_M_functor, _M_functor, __destroy_functor); 508 _M_manager = nullptr; 509 _M_invoker = nullptr; 510 } 511 return *this; 512 } 513 514 /** 515 * @brief Function assignment to a new target. 516 * @param __f A function object that is callable with parameters of 517 * type `_ArgTypes...` and returns a value convertible 518 * to `_Res`. 519 * @return `*this` 520 * @since C++11 521 * 522 * This function object wrapper will target a copy of `__f`. If `__f` 523 * is `reference_wrapper<F>`, then this function object will contain 524 * a reference to the function object `__f.get()`. If `__f` is a null 525 * function pointer or null pointer-to-member, this object will be 526 * empty. 527 * 528 * If `__f` is a non-null function pointer or an object of type 529 * `reference_wrapper<F>`, this function will not throw. 530 */ 531 template<typename _Functor> 532 _Requires<_Callable<_Functor>, function&> 533 operator=(_Functor&& __f) 534 noexcept(_Handler<_Functor>::template _S_nothrow_init<_Functor>()) 535 { 536 function(std::forward<_Functor>(__f)).swap(*this); 537 return *this; 538 } 539 540 /// @overload 541 template<typename _Functor> 542 function& 543 operator=(reference_wrapper<_Functor> __f) noexcept 544 { 545 function(__f).swap(*this); 546 return *this; 547 } 548 549 // [3.7.2.2] function modifiers 550 551 /** 552 * @brief Swap the targets of two %function objects. 553 * @param __x A %function with identical call signature. 554 * 555 * Swap the targets of `this` function object and `__f`. 556 * This function will not throw exceptions. 557 */ 558 void swap(function& __x) noexcept 559 { 560 std::swap(_M_functor, __x._M_functor); 561 std::swap(_M_manager, __x._M_manager); 562 std::swap(_M_invoker, __x._M_invoker); 563 } 564 565 // [3.7.2.3] function capacity 566 567 /** 568 * @brief Determine if the %function wrapper has a target. 569 * 570 * @return `true` when this function object contains a target, 571 * or `false` when it is empty. 572 * 573 * This function will not throw exceptions. 574 */ 575 explicit operator bool() const noexcept 576 { return !_M_empty(); } 577 578 // [3.7.2.4] function invocation 579 580 /** 581 * @brief Invokes the function targeted by `*this`. 582 * @returns the result of the target. 583 * @throws `bad_function_call` when `!(bool)*this` 584 * 585 * The function call operator invokes the target function object 586 * stored by `this`. 587 */ 588 _Res 589 operator()(_ArgTypes... __args) const 590 { 591 if (_M_empty()) 592 __throw_bad_function_call(); 593 return _M_invoker(_M_functor, std::forward<_ArgTypes>(__args)...); 594 } 595 596 #if __cpp_rtti 597 // [3.7.2.5] function target access 598 /** 599 * @brief Determine the type of the target of this function object 600 * wrapper. 601 * 602 * @returns the type identifier of the target function object, or 603 * `typeid(void)` if `!(bool)*this`. 604 * 605 * This function will not throw exceptions. 606 */ 607 const type_info& 608 target_type() const noexcept 609 { 610 if (_M_manager) 611 { 612 _Any_data __typeinfo_result; 613 _M_manager(__typeinfo_result, _M_functor, __get_type_info); 614 if (auto __ti = __typeinfo_result._M_access<const type_info*>()) 615 return *__ti; 616 } 617 return typeid(void); 618 } 619 #endif 620 621 /** 622 * @brief Access the stored target function object. 623 * 624 * @return Returns a pointer to the stored target function object, 625 * if `typeid(_Functor).equals(target_type())`; otherwise, a null 626 * pointer. 627 * 628 * This function does not throw exceptions. 629 * 630 * @{ 631 */ 632 template<typename _Functor> 633 _Functor* 634 target() noexcept 635 { 636 const function* __const_this = this; 637 const _Functor* __func = __const_this->template target<_Functor>(); 638 // If is_function_v<_Functor> is true then const_cast<_Functor*> 639 // would be ill-formed, so use *const_cast<_Functor**> instead. 640 return *const_cast<_Functor**>(&__func); 641 } 642 643 template<typename _Functor> 644 const _Functor* 645 target() const noexcept 646 { 647 if _GLIBCXX17_CONSTEXPR (is_object<_Functor>::value) 648 { 649 // For C++11 and C++14 if-constexpr is not used above, so 650 // _Target_handler avoids ill-formed _Function_handler types. 651 using _Handler = _Target_handler<_Res(_ArgTypes...), _Functor>; 652 653 if (_M_manager == &_Handler::_M_manager 654 #if __cpp_rtti 655 || (_M_manager && typeid(_Functor) == target_type()) 656 #endif 657 ) 658 { 659 _Any_data __ptr; 660 _M_manager(__ptr, _M_functor, __get_functor_ptr); 661 return __ptr._M_access<const _Functor*>(); 662 } 663 } 664 return nullptr; 665 } 666 /// @} 667 668 private: 669 using _Invoker_type = _Res (*)(const _Any_data&, _ArgTypes&&...); 670 _Invoker_type _M_invoker = nullptr; 671 }; 672 673 #if __cpp_deduction_guides >= 201606 674 template<typename> 675 struct __function_guide_helper 676 { }; 677 678 template<typename _Res, typename _Tp, bool _Nx, typename... _Args> 679 struct __function_guide_helper< 680 _Res (_Tp::*) (_Args...) noexcept(_Nx) 681 > 682 { using type = _Res(_Args...); }; 683 684 template<typename _Res, typename _Tp, bool _Nx, typename... _Args> 685 struct __function_guide_helper< 686 _Res (_Tp::*) (_Args...) & noexcept(_Nx) 687 > 688 { using type = _Res(_Args...); }; 689 690 template<typename _Res, typename _Tp, bool _Nx, typename... _Args> 691 struct __function_guide_helper< 692 _Res (_Tp::*) (_Args...) const noexcept(_Nx) 693 > 694 { using type = _Res(_Args...); }; 695 696 template<typename _Res, typename _Tp, bool _Nx, typename... _Args> 697 struct __function_guide_helper< 698 _Res (_Tp::*) (_Args...) const & noexcept(_Nx) 699 > 700 { using type = _Res(_Args...); }; 701 702 #if __cpp_explicit_this_parameter >= 202110L 703 // _GLIBCXX_RESOLVE_LIB_DEFECTS 704 // 3617. function/packaged_task deduction guides and deducing this 705 template<typename _Res, typename _Tp, bool _Nx, typename... _Args> 706 struct __function_guide_helper<_Res (*) (_Tp, _Args...) noexcept(_Nx)> 707 { using type = _Res(_Args...); }; 708 #endif 709 710 #if __cpp_static_call_operator >= 202207L && __cpp_concepts >= 202002L 711 template<typename _StaticCallOp> 712 struct __function_guide_static_helper 713 { }; 714 715 template<typename _Res, bool _Nx, typename... _Args> 716 struct __function_guide_static_helper<_Res (*) (_Args...) noexcept(_Nx)> 717 { using type = _Res(_Args...); }; 718 719 template<typename _Fn, typename _Op> 720 using __function_guide_t = typename __conditional_t< 721 requires (_Fn& __f) { (void) __f.operator(); }, 722 __function_guide_static_helper<_Op>, 723 __function_guide_helper<_Op>>::type; 724 #else 725 template<typename _Fn, typename _Op> 726 using __function_guide_t = typename __function_guide_helper<_Op>::type; 727 #endif 728 729 template<typename _Res, typename... _ArgTypes> 730 function(_Res(*)(_ArgTypes...)) -> function<_Res(_ArgTypes...)>; 731 732 template<typename _Fn, typename _Signature 733 = __function_guide_t<_Fn, decltype(&_Fn::operator())>> 734 function(_Fn) -> function<_Signature>; 735 #endif 736 737 // [20.7.15.2.6] null pointer comparisons 738 739 /** 740 * @brief Test whether a polymorphic function object wrapper is empty. 741 * @returns `true` if the wrapper has no target, `false` otherwise 742 * 743 * This function will not throw exceptions. 744 */ 745 template<typename _Res, typename... _Args> 746 inline bool 747 operator==(const function<_Res(_Args...)>& __f, nullptr_t) noexcept 748 { return !static_cast<bool>(__f); } 749 750 #if __cpp_impl_three_way_comparison < 201907L 751 /// @overload 752 template<typename _Res, typename... _Args> 753 inline bool 754 operator==(nullptr_t, const function<_Res(_Args...)>& __f) noexcept 755 { return !static_cast<bool>(__f); } 756 757 /** 758 * @brief Test whether a polymorphic function object wrapper is non-empty. 759 * @returns `false` if the wrapper has no target, `true` otherwise 760 * 761 * This function will not throw exceptions. 762 */ 763 template<typename _Res, typename... _Args> 764 inline bool 765 operator!=(const function<_Res(_Args...)>& __f, nullptr_t) noexcept 766 { return static_cast<bool>(__f); } 767 768 /// @overload 769 template<typename _Res, typename... _Args> 770 inline bool 771 operator!=(nullptr_t, const function<_Res(_Args...)>& __f) noexcept 772 { return static_cast<bool>(__f); } 773 #endif 774 775 // [20.7.15.2.7] specialized algorithms 776 777 /** 778 * @brief Swap the targets of two polymorphic function object wrappers. 779 * 780 * This function will not throw exceptions. 781 */ 782 // _GLIBCXX_RESOLVE_LIB_DEFECTS 783 // 2062. Effect contradictions w/o no-throw guarantee of std::function swaps 784 template<typename _Res, typename... _Args> 785 inline void 786 swap(function<_Res(_Args...)>& __x, function<_Res(_Args...)>& __y) noexcept 787 { __x.swap(__y); } 788 789 #if __cplusplus >= 201703L 790 namespace __detail::__variant 791 { 792 template<typename> struct _Never_valueless_alt; // see <variant> 793 794 // Provide the strong exception-safety guarantee when emplacing a 795 // function into a variant. 796 template<typename _Signature> 797 struct _Never_valueless_alt<std::function<_Signature>> 798 : std::true_type 799 { }; 800 } // namespace __detail::__variant 801 #endif // C++17 802 803 _GLIBCXX_END_NAMESPACE_VERSION 804 } // namespace std 805 806 #endif // C++11 807 #endif // _GLIBCXX_STD_FUNCTION_H
