import collection.mutable

class MySet(self:mutable.Set[String]) extends mutable.Set[String] with mutable.SetLike[String, MySet]{

  override def -=(elem: String) = {self -= elem; this}
  override def +=(elem: String) = {self += elem; this}

  override def empty = new MySet(self.empty)
  override def iterator = self.iterator
  override def contains(elem: String) = self.contains(elem)
}

val s = new MySet(mutable.Set("EXPOSEDNODE", "CONNECTABLE"))
s.clear()
println(s) // prints "Set(CONNECTABLE)"