Extends Java enums so Scala match statements work. The purpose of this code example is to show a generic way of extending multiple Java enums in a Scala program so Scala match statements work, while preserving all of the functionality of Java enums for use by Scala programs. That is why there are methods that are defined but not used. A macro co…

BlendedEnums.scala

object BlendedEnums extends App {
  import Day._

  trait EnumLike[T] extends Ordered[T] {
    def name: String

    def compare(other: T): Int

    def ordinal: Int

    def toString: String
  }

  sealed class CaseDay(val day: Day) extends EnumLike[Day] {
    lazy val name: String = day.name

    def compare(other: Day): Int = day.compareTo(other)

    lazy val ordinal: Int = day.ordinal

    override lazy val toString = day.toString
  }

  object CaseDay {
    import scala.collection.immutable.{SortedSet, TreeSet}

    case object Monday extends CaseDay(MONDAY)
    case object Tuesday extends CaseDay(TUESDAY)
    case object Wednesday extends CaseDay(WEDNESDAY)
    case object Thursday extends CaseDay(THURSDAY)
    case object Friday extends CaseDay(FRIDAY)
    case object Saturday extends CaseDay(SATURDAY)
    case object Sunday extends CaseDay(SUNDAY)

    def valueOf(name: String) = Day.valueOf(name)

    type CaseDayObject = CaseDay with Product with Serializable
    lazy val values: SortedSet[CaseDayObject] = {
      val ordering = Ordering.by { caseDayObject: CaseDayObject ⇒ caseDayObject.ordinal }
      TreeSet(Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday)(ordering)
    }
  }

  import CaseDay._
  def tellItLikeItIs(theDay: CaseDay): Unit = {
    val msg = theDay match {
      case Monday => "Mondays are bad."
      case Friday => "Fridays are better."
      case Saturday => "Weekends are best."
      case Sunday => "Weekends are best."
      case _ => "Midweek days are so-so."
    }
    println(msg)
  }
  tellItLikeItIs(Monday)
  tellItLikeItIs(Tuesday)
  tellItLikeItIs(Wednesday)
  tellItLikeItIs(Sunday)
}

Day.java

public enum Day {
    SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY 
}