From cppreference.com
move_only_function&operator=(move_only_function&&other); (1) (since C++23)move_only_function&operator=(constmove_only_function&)=delete; (2) (since C++23)move_only_function&operator=(std::nullptr_t)noexcept; (3) (since C++23)template<classF>move_only_function&operator=(F&&f); (4) (since C++23)Assigns a new target to std::move_only_function or destroys its target.
1) Moves the target of other to *this or destroys the target of *this (if any) if other is empty, by auto(std::move(other)).swap(*this). other is in a valid state with an unspecified value after move assignment.
2) Copy assignment operator is deleted. std::move_only_function does not satisfy
.
3) Destroys the current target if it exists. *this is empty after the call.
4) Sets the target of *this to the callable f, or destroys the current target if f is a null function pointer, a null pointer to member function, or an empty std::move_only_function, as if by executing move_only_function(std::forward<F>(f)).swap(*this);. This overload participates in overload resolution only if the constructor of move_only_function from F participates in overload resolution. The program is ill-formed or has undefined behavior if the selected constructor call is ill-formed or has undefined behavior.
Parameters
other - another std::move_only_function object to move the target of f - a callable object to initialize the new target with Return value
*this
Notes
It is intentional not to require the move assignment operator to be noexcept to leave room for an allocator-aware move_only_function in future.
move_only_function can be assigned from std::in_place_type<Fn> given it can be constructed from that argument.
Example
See also
assigns a new target
(public member function of std::function<R(Args...)>)