Model ADT

Model.scala

sealed trait Id[T <: Id[T]]

trait Mid[T <: Mid[T]] extends Id[Mid[T]]

trait Sid[T <: Mid[T]] extends Id[Sid[T]]

case class AMid() extends Mid[AMid]

case class CSid() extends Sid[AMid]

// I wish to get rid of the _
case class E[T <: Sid[_]](s: T) extends Id[E[T]]

val amid = AMid()
val csid = CSid()
val e = E(csid)

test.scala

def unapply(): Option[E[_]] = {
  Some(e)
}