Better Enumerations in Scala

BetterEnums.scala

/**
 * A base trait for custom enumerations
 *
 * <ol>
 *   <li>Have an abstract super class E for all your enum items.</li>
 *   <li>Generate case objects for each enumeration item of type E.</li>
 *   <li>Then add them to values set when you implement it.</li>
 * </ol>
 *
 * Example:
 * {{{
 *   object Animals extends EnumBase[Animals.Animal] {
 *     abstract class Animal(val legs: Int)
 *
 *     case object Chicken extends Animal(legs = 2)
 *     case object Cat     extends Animal(legs = 4)
 *     case object Ant     extends Animal(legs = 6)
 *
 *     override val values: Set[Animals.Animal] = Set(Chicken, Cat, Ant)
 *   }
 * }}}
 *
 * @tparam E Type of items in the enum
 */
trait EnumBase[E] {
  /** Set of enumeration values, you need to override this in your enumeration object! */
  val values: Set[E]

  /** A mapping from enumeration item name to item itself */
  protected lazy val valueMap: Map[String, E] = values.map(v => v.toString -> v).toMap

  /**
   * Returns enumeration item by it's name optionally
   *
   * @param name Name of the enumeration item
   *
   * @return Option(item) if found, None if not found
   */
  def withName(name: String): Option[E] = valueMap.get(name)
}

object Animals extends EnumBase[Animals.Animal] {
  abstract class Animal(val legs: Int)

  case object Chicken extends Animal(legs = 2)
  case object Cat     extends Animal(legs = 4)
  case object Ant     extends Animal(legs = 6)

  override val values: Set[Animal] = Set(Chicken, Cat, Ant)
}

object Demo {
  def main (args: Array[String]) {
    // Get all values in an enumeration
    println("All Animals: " + Animals.values)

    // Get a field of an enumeration item
    println("Number of legs of Chicken: " + Animals.Chicken.legs)

    // Get an enumeration item by it's name
    println("Number of legs of Animal named \"Ant\": " + Animals.withName("Ant").get.legs)

    // Cannot get an enumeration item by it's name
    println("Is there an Animal named \"Foo\"?: " + Animals.withName("Foo").isDefined)

    // Do pattern matching over enumeration
    print("Pattern matching an animal: ")
    val animal: Animals.Animal = Animals.Ant
    animal match {
      case a: Animals.Chicken.type => println("Chicken")
      case a: Animals.Cat.type => println("Cat")
      case a: Animals.Ant.type => println("Ant")
    }
  }
}