Foo.scala

// Is there a way to do this such that we don't end up with List[Thing[_]],
// but instead end up with something with the types preserved?
object Foo {
  sealed trait Thing[T]
  case class IntThing(i: Int) extends Thing[Int]
  case class StringThing(s: String) extends Thing[String]
  case class DoubleThing(d: Double) extends Thing[Double]

  // The implementation here is only to get a compile
  def differentThingsKnownOnlyAtRuntime(i: Int): Thing[_] = i match {
    case 0 ⇒ IntThing(0)
    case 1 ⇒ StringThing("Hello")
    case 2 ⇒ DoubleThing(1.0)
  }

  val foo: List[Thing[_]] = (0 to 2).toList map differentThingsKnownOnlyAtRuntime
}