Generic scala trait

I need to write a generic trait, which can return the class of its generic type. Here is what I am trying to implement, but I can't get it to compile:

trait MyTrait[T] {
  implicit def classTagT: ClassTag[T]

  def foo(t: T): Unit
  def getType(): Class[T] = classTagT.runtimeClass
}

What is the best way to accomplish this? Should I be writing a macro instead?