Custom Orderings

Ordering.scala

sealed abstract class Bound[+T] {  val value : T  }
case class Closed[T : Ordering](value : T) extends Bound[T]
case class Opened[T : Ordering](value : T) extends Bound[T]

object Bound {
  implicit def ordering[T: Ordering]: Ordering[Bound[T]] = Ordering.by((_: Bound[T]).value)
}

object BoundDemo {
 def main(args : Array[String]) : Unit = {
   val order = implicitly[Ordering[Bound[Int]]]
   import order._

   // todo : Create an ordering on `Bound[T]`
   assert((Closed(1)  < Closed(10)) == true)
   assert((Closed(10) > Opened(10)) == true)

   def optionOrder[X: Ordering] = Ordering.by( (_: Option[X]) match {
     case Some(_) => 1
     case None    => 0
   })
   val bOptionOrder = optionOrder[Bound[Int]]
   import bOptionOrder._

   // todo : Create an ordering on `Option[Bound[T]]`
   assert((Some(Closed(1))  < Some(Closed(10))) == true)
   assert((Some(Closed(10)) > Some(Opened(10))) == true)
 }
}