class Bar extends Ordered[Bar] {
  val id = Bar.add(this) // yields bug; maybe compiler should forbid to use "this" as long as it is not initialized??
  // this works: val id = Bar.nextId; Bar.collec += this
  override def compare(that: Bar) = this.id - that.id
  override def toString() = "" + id
}

object Bar {
  val collec = new scala.collection.jcl.TreeSet[Bar]
  var id = 0
  def nextId: Int = {id = id + 1; id}
  def add(bar: Bar): Int = {collec += bar; nextId}
}

object Foo {
  def main(args: Array[String]) {
    val bars = List(1,2,3,4,5).map(a => new Bar())
    Bar.collec -= bars(2)
    Console.println("" + Bar.collec)
  }
}