Phantom Types

phantomtypes.scala

object console extends App {

  trait Op
  trait Open extends Op
  trait Close extends Op

  trait Door[O <: Op]
  object Door {
    def apply[S <: Op] = new Door[S] {}

    def open[S <: Close](d: Door[S]) = Door[Open]
    def close[S <: Open](d: Door[S]) = Door[Close]
  }

  val closeDoor = Door[Close]
  val openDoor = Door.open(closeDoor)
  val closeAgainDoor = Door.close(openDoor)

  // val closeCloseDoor = Door.close(closeDoor)
  // val openOpenDoor = Door.open(openDoor)
}