Unapply.scala

trait A

case object a extends A
case object b extends A

trait B

case object x extends B
case object y extends B

object A {
  def apply(arg: B): A = arg match {
    case x => a
    case y => b
  }

  def unapply(arg: A): Option[B] = arg match {
    case a => Some(x)
    case b => Some(y)
    case _ => None
  }
}


object Unapply {
  def main(args: Array[String]): Unit = {
    val arg: A = a
    arg match {
      case x => println("x")
      case y => println("y")
    }
  }
}