Why this is exhaustive ``` fun <T> Tree<T...

# announcements

[Dmitry Kandalov]

Why this is exhaustive

fun <T> Tree<T>.nodes(): List<Node<T>> =
    when (this) {
        is Node<T> -> left.nodes() + right.nodes() + this
        is End        -> emptyList()
    }

but this is not

fun <T> Tree<T>.nodes(): List<Node<T>> =
    when {
        this is Node<T> -> left.nodes() + right.nodes() + this
        this is End     -> emptyList()
        // kotlin wants `else` here
    }

?