Amusingly (to me, at least), I took a stab a long time ago to show how a visitor could get you most of this. As I state in the post, I make no claim that this

Amusingly (to me, at least), I took a stab a long time ago to show how a visitor could get you most of this. As I state in the post, I make no claim that this is as convenient or powerful. It does do what you basically describe, though. https://taeric.github.io/sum-types.html https://taeric.github.io/sum-types.html Note instead of my worse Optional class, what you are describing is a Shape class where there is a different function for each supported shape. If you add a new shape, everywhere that made a shape visitor would have to be updated do deal with the new shape. (A sibling post described this.) Amusingly, I recall coworkers that did not want to use the "acceptVisitor" method and would force cast to call over to the methods directly. Caught me incredibly off guard.