Enumerated types and extending existing types in Scala 2/3

2022-11-12 scala

Scala 2

Scala 2 doesn’t have an enum like Java, so Enumeration or case object are used. Besides, you can add fields to existing types by importing implicit class,

sealed trait Animal

object Animal {
  case object Dog extends Animal
  case object Cat extends Animal
}

object Converter {
  implicit class AnimalConverter(animal: Animal) {
    def hello() = animal match {
      case Animal.Dog => "wan!"
      case Animal.Cat => "nya!"
    }
  }
}

import Converter.AnimalConverter

object App {
  def main() = {
    print(Animal.Cat.hello) // nya!
  }
}

Scala 3

enum and extension were added in Scala 3, so you can write as follows.

enum Animal:
  case Dog, Cat

extension (animal: Animal) {
  def hello() = animal match {
    case Animal.Dog => "wan!"
    case Animal.Cat => "nya!"
  }
}

object App {
  def main() = {
    print(Animal.Cat.hello()) // nya!
  }
}