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std::function::function(3) C++ Standard Libary std::function::function(3) NAME std::function::function - std::function::function Synopsis function() noexcept; (1) (since C++11) function( std::nullptr_t ) noexcept; (2) (since C++11) function( const function& other ); (3) (since C++11) function( function&& other ); (since C++11) (un- til C++20) function( function&& other ) noexcept; (since C++20) template< class F > (5) (since C++11) function( F&& f ); template< class Alloc > (since C++11) function( std::allocator_arg_t, const Alloc& (6) (removed in C++17) alloc ) noexcept; template< class Alloc > function( std::allocator_arg_t, const Alloc& (7) (since C++11) alloc, (removed in C++17) std::nullptr_t ) noexcept; template< class Alloc > (4) function( std::allocator_arg_t, const Alloc& (8) (since C++11) alloc, (removed in C++17) const function& other ); template< class Alloc > function( std::allocator_arg_t, const Alloc& (9) (since C++11) alloc, (removed in C++17) function&& other ); template< class F, class Alloc > (since C++11) function( std::allocator_arg_t, const Alloc& (10) (removed in C++17) alloc, F f ); Constructs a std::function from a variety of sources. 1,2) Creates an empty std::function. 3) Copies the target of other to the target of *this. If other is empty, *this will be empty right after the call too. 4) Moves the target of other to the target of *this. If other is empty, *this will be empty right after the call too. other is in a valid but unspecified state right after the call. 5) Initializes the target with std::forward<F>(f). The target is of type std::decay<F>::type. If f is a null pointer to function, a null pointer to member, or an empty value of some std::function specialization, *this will be empty right after the call. This overload participates in overload resolution only if all fol- lowing conditions are satisfied: * std::is_same_v<std::remove_cvref_t<F>, std::function<R(Args...)> (since C++23) is false. * An lvalue of type std::decay<F>::type is callable for argument types Args... and return type R. If std::is_copy_constructible_v<std::decay_t<F>> or std::is_constructible_v<std::decay_t<F>, F> is false, the program is (since C++23) ill-formed. If F is not CopyConstructible, the behavior is undefined. 6-10) Same as (1-5) except that alloc is used to allocate memory for any internal data structures that the std::function might use. When the target is a function pointer or a std::reference_wrapper, small object optimization is guaranteed, that is, these targets are always di- rectly stored inside the std::function object, no dynamic allocation takes place. Other large objects may be constructed in dynamic allocated storage and accessed by the std::function object through a pointer. Parameters other - the function object used to initialize *this f - a callable object used to initialize *this alloc - an Allocator used for internal memory allocation Type requirements - Alloc must meet the requirements of Allocator. Exceptions 3,8,9) Does not throw if other's target is a function pointer or a std::reference_wrapper, otherwise may throw std::bad_alloc or any exception thrown by the constructor used to copy or move the stored callable object. 4) Does not throw if other's target is a function pointer or a std::reference_wrapper, otherwise may throw std::bad_alloc or any (until C++20) exception thrown by the constructor used to copy or move the stored callable object. 5,10) Does not throw if f is a function pointer or a std::refer- ence_wrapper, otherwise may throw std::bad_alloc or any exception thrown by the copy constructor of the stored callable object. Notes std::function's allocator support was poorly specified and inconsis- tently implemented. Some implementations do not provide overloads (6-10) at all, some provide the overloads but ignore the supplied allocator argument, and some provide the overloads and use the supplied allocator for construction but not when the std::function is reassigned. As a result, allocator support was re- moved in C++17. Example This section is incomplete Reason: no example Defect reports The following behavior-changing defect reports were applied retroac- tively to previously published C++ standards. DR Applied to Behavior as published Correct be- havior LWG 2132 C++11 overloads (5,10) might be ambiguous constrained LWG 2774 C++11 (5,10) performed an additional move eliminated See also constructor constructs a new std::move_only_function object (C++23) (public member function of std::move_only_function) Category: * Todo no example http://cppreference.com 2024.06.10 std::function::function(3)
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