Call Visitor class on arrays
auto apply_visitor(Array a, V visitor) dispatch to visitor class
operations based on array type.
apply_visitor to pass in an instance of Array or one of its
subclasses and a visitor functor, and invoke the operator() method, which must be
defined in the user-defined functor, with the appropriate concrete array type.
|visitor class V&&|
The user-supplied visitor object, passed:
Outputs returned by the visitor.