@Bob Well the compiler already does this for normal if statements on sealed classes, so it's not really a problem if there are many of them.

karelpeeters: does what exactly?

It looks like my memory failed me, I thought this worked:

sealed class Base

class A(val a: String) : Base()
class B(val b: String) : Base()

fun foo(base: Base) {
    if (base is A) {
        print(base.a)
    } else {
        print(base.b)
    }
}

But is doesn't...