function& operator=( const function& other );
(1) (since C++11)
function& operator=( function&& other );
(2) (since C++11)
function& operator=( std::nullptr_t ) noexcept;
(3) (since C++11)
template< class F > 
function& operator=( F&& f );
(4) (since C++11)
template< class F > 
function& operator=( std::reference_wrapper<F> f ) noexcept;
(5) (since C++11)

Assigns a new target to std::function.

1) Assigns a copy of target of other, as if by executing function(other).swap(*this);
2) Moves the target of other to *this. other is in a valid state with an unspecified value.
3) Drops the current target. *this is empty after the call.
4) Sets the target of *this to the callable f, as if by executing function(std::forward<F>(f)).swap(*this);. This operator does not participate in overload resolution unless f is Callable for argument types Args... and return type R.
5) Sets the target of *this to a copy of f, as if by executing function(f).swap(*this);


other - another std::function object to copy the target of
f - a callable to initialize the target with
Type requirements
-F must meet the requirements of Callable.

Return value



Even before allocator support was removed from std::function in C++17, these assignment operators use the default allocator rather than the allocator of *this or the allocator of other (see LWG issue 2386).

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 2132 C++11 the overload taking a Callable object might be ambiguous constrained
LWG 2401 C++11 assignment operator from std::nullptr_t not required to be noexcept required

See also

replaces or destroys the target
(public member function of std::move_only_function)
(removed in C++17)
assigns a new target
(public member function)

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