I've gotten far with type switching on an interface that amounts to a single function that does nothing. Unfortunately it does nothing in terms of exhaustivene

I've gotten far with type switching on an interface that amounts to a single function that does nothing. Unfortunately it does nothing in terms of exhaustiveness, but it effectively gives you sum types which IME are so, so much easier to work with than state pattern or other inject-an-object-abstractions. Not having to design an API (that later leaks) is rewarding enough. It's strangely efficient as well. I've experimented with implementing sum types via tagged C-style unions and at every (ad hoc, micro) benchmark I've tried them against, type switching on an interface comes out on top.