std::function::operator() (3) Linux Manual Page

std::function<R(Args…)>::operator= – std::function<R(Args…)>::operator=

Synopsis

function &operator=(const function &other);
(1)(since C++ 11)

    function &
    operator=(function &&other);
(2)(since C++ 11)

    function &
    operator=(std::nullptr_t);
(since C++ 11)(until C++ 17)

    function &
    operator=(std::nullptr_t) noexcept;
(since C++ 17)

    template <class F>
    (3)(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.

    (since C++ 14)

        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_#2386).

See also

assign assigns a new target
              (public member function)
(until C++17)