Hey there; Just a little question: Why is this an unchecked cast?

val items = mutableListOf<T>()

override fun <U : T> typedItems(): List<U> {
    return items.mapNotNull { it as? U }
}

but this is not?

val oldStuff = mutableListOf<List<*>>()
val newStuff = oldStuff.mapNotNull { it as? ArrayList<*> }

Because of jvm type erasure at runtime, the cast is unchecked, because it cannot check that the type is U So the cast will succeed and might lead to a runtime error elsewhere.

Got it, alright!