问Scala:抽象类型的typeTag？

EN

trait Sim {
    type Probe
    var probe: Probe

    def reflectProbe() {
      // works: 
      val tt_int = scala.reflect.runtime.universe.typeTag[Int]
      // does not work (No TypeTag available for Sim.this.Probe):
      val tt_probe = scala.reflect.runtime.universe.typeTag[Probe]
    }
}

class WorldProbe

class World extends Sim {
  type Probe = WorldProbe
  var probe: Probe = new WorldProbe
}