NAME

std::function::operator= - std::function::operator=

Synopsis

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 > (4) (since C++11)
function& operator=( F&& f );
template< class F > (5) (since C++11)
function& operator=( std::reference_wrapper<F> f ) noexcept;

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 constrained
ambiguous
LWG 2401 C++11 assignment operator from std::nullptr_t not required
required to be noexcept

See also

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