Attempt to a typesafe factory patter in scala

Factory.scala

/**
 * Created by claramun on 6/9/14.
 */

trait A
trait B { val value:String }

trait X1A extends A
trait X1B extends B

trait X2A extends A
trait X2B extends B

trait X{
  type A1  <: A
  type B1  <: B

  val in:A1

  def xx(a:A1):B1


}

object X1 extends X{
  type A1 = X1A
  type B1 = X1B

  val in = new X1A {}

  def xx(a:A1):B1 = {
    new X1B{ val value = "X1B ="+a }
  }
}

object X2 extends X{
  type A1 = X2A
  type B1 = X2B

  val in = new X2A {}

  def xx(a:A1):B1 = {
    new X2B{ val value = "X2B ="+a }
  }
}

object Factory {

  def build(x:Any):X= x match {
    case i:Int => X1
    case s:String => X2
  }
}

object Run extends App {
  val x1=Factory.build(1)
  val x2= Factory.build("a")
  println("1 "+x1.xx(x1.in).value)
  println("a "+x2.xx(x2.in).value)
}