Beither

Beither.scala

abstract class Beither[+A, +B] {
  // From German "beide" and English "either" => "beither".
  // Preferably pronounced as German "Beißer".

  def left = Beither.LeftProjection(this)

  def right = Beither.RightProjection(this)

  def both = Beither.BothProjection(this)
}

case class Left[+A, +B](a: A) extends Beither[A, B]

case class Right[+A, +B](b: B) extends Beither[A, B]

case class Both[+A, +B](a: A, b: B) extends Beither[A, B]

object Beither {

  case class BothProjection[+A, +B](e: Beither[A, B]) {
    def get = e match {
      case Both(a, b) => (a, b)
      case _ => throw new NoSuchElementException("Beither.both.value on Right or Left")
    }
  }

  case class LeftProjection[+A, +B](e: Beither[A, B]) {
    def get = e match {
      case Left(a) => a
      case Both(a, _) => a
      case Right(_) => throw new NoSuchElementException("Beither.left.value on Right")
    }
  }

  case class RightProjection[+A, +B](e: Beither[A, B]) {
    def get = e match {
      case Left(_) => throw new NoSuchElementException("Beither.right.value on Left")
      case Right(b) => b
      case Both(_, b) => b
    }
  }

}

val a: Beither[String, Int] = Right(1)
val b: Beither[String, Int] = Left("a")
val c: Beither[String, Int] = Both("a", 1)

c.left.get // String = a
c.right.get // Int = 1
c.both.get // (String, Int) = (a,1)