There is subtyping. A more practical (though not necessarily realistic) example might be: sealed interface List<T> permits Cons<T>, None<T> { record Con

There is subtyping. A more practical (though not necessarily realistic) example might be: sealed interface List<T> permits Cons<T>, None<T> { record Cons<T>(T head, List<T> tail) {} record None<T>() {} } // some function only wanting the first elem of a list switch (List<T> list) { case Cons<>(T head, var tail) -> // do something default -> {} } If you have used Haskell or similarly strongly typed FP language, you can see how great pattern matching can be.