path dependent types and unapply

TypeIndexing.scala

  trait A {
    type T
    val t : T
  }

  object A {
    def unapply(arg: A): Option[arg.T] = Some(arg.t)
  }

  def use(a : A) = a match  {
    case A(t) ⇒
      val s: a.T = t // type mismatch.
                     // found t.type (with underlying type <unapply-selector>.T)
                     // required: a.T
  }