1.scala

sealed trait Value
sealed trait Prim[A] extends Value {
  def value: A
}
case class StringPrim(value: String) extends Prim[String]
val x: Value = StringPrim("hi")

def get[A](v: Value): Option[A] = v match {
  case p: Prim[A] => Some(p.value)
  case _ => None
}

// scala> get[String](x)
// res0: Option[String] = Some(hi)
// scala> get[Int](x)
// res1: Option[Int] = Some(hi)

def get2[A](v: Value)(implicit tag: scala.reflect.ClassTag[A]): Option[A] = v match {
  case p: Prim[A] if p.value.getClass == tag.runtimeClass => Some(p.value)
  case _ => None
}

// scala> get2[String](x)
// res0: Option[String] = Some(hi)
// scala> get2[Int](x)
// res1: Option[Int] = None