abstract class A {
    abstract fun doStuffWithOther(other: A)

    protected fun sayHi() {
        println("hi!")
    }
}

class B : A() {
    override fun doStuffWithOther(other: A) {
        sayHi() // this compiles
        other.sayHi() // this is angry
    }
}

fun main(args: Array<String>) {
    B().doStuffWithOther(B())
}