retronym

class RichOrdering[A](oa: Ordering[A]) {
  def thenBy[B: Ordering](f: A => B): Ordering[A] = new Ordering[A] {
    def compare(a1: A, a2: A) = oa.compare(a1, a2) match {
      case 0 => Ordering[B].compare(f(a1), f(a2))
      case x => x
    }
  }
}

implicit def ToRichOrdering[A](oa: Ordering[A]): RichOrdering[A] = new RichOrdering(oa)