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 -> {}
}
Re:Java 21: What’s New?
by heavyset_go on Thursday August 10, 2023 @04:52PM
(#37081631)
> Sure, but in Java the standard handling of that is polymorphism. instanceof has been so far a bit of an antipattern, breaking out of the OOP model.
I think that's deliberate, Java is moving towards the modern programming zeitgeist that doesn't really care about strict adherence to the OOP model. This is a feature that comes from languages that don't adhere to Java's OOP principles.
I didn't downvote you, by the way. Don't know why that happened.
Sure, but in Java the standard handling of that is polymorphism. instanceof has been so far a bit of an antipattern, breaking out of the OOP model.
> In your example there is no reason to use `instanceof` with `p`, you already know what it is.
That's my point. This seems like a very limited version of destructuring if you can use it only when you don't know the type. Like in JavaScript you'd routinely write something like: