std::function<R(Args...)>::assign

template< class F, class Alloc >
void assign( F&& f, const Alloc& alloc );

(since C++11)
(removed in C++17)

Initializes the target with f. alloc is used to allocate memory for any internal data structures that the function might use.

Equivalent to function(allocator_arg, alloc, std::forward<F>(f)).swap(*this).

f	-	callable function to initialize the target with
alloc	-	allocator to use to allocate memory for the internal data structures

(none).

(none).