[scala] Structural types within classes with contravariant type parameters are unsound

Hi,

Consider the following code:
////////////////////////////////////////
class A[-S](y : S) {
  val f  = new { val x = y }
}
////////////////////////////////////////

It compiles without any errors. But now we can write:

scala> val a = new A(1)
a: A[Int] = A@43e3ac

scala> val b = a : A[Nothing]
b: A[Nothing] = A@43e3ac

scala> b.f.x
java.lang.ClassCastException: java.lang.Integer cannot be cast to
scala.runtime.Nothing$
        at .<init>(<console>:8)
        at .<clinit>(<console>)
        at RequestResult$.<init>(<console>:4)
        at RequestResult$.<clinit>(<console>)
        at RequestResult$result(<console>)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorIm...

Looks like unsoundness.

Thanks,
Vladimir