This is the kind of OG way to do it even before we had patterns. There are a couple of problems with it, least of which is that I can't then use one or both of those in a wider union elsewhere, because their definitions are bound to that parent class. Ideally I'd like to see something very similar to the linked OneOf library. That allows you to do both in-line definitions OR subclass from OneOf<T1,T2,T3...> to reify the union as a class as well. If that is done and integrated properly into the pattern matching system, I believe it will yield very powerful expressiveness.