# std::function<R(Args...)>::operator=

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< cpp‎ | utility‎ | functional‎ | function

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);

### Parameters

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

*this

### Notes

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

operator= (C++23) | replaces or destroys the target (public member function of `std::move_only_function`)
assign (removed in C++17) | assigns a new target (public member function)

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