期权匹配的Scala类型擦除

object Test {
  def main(args: Array[String]) {
    val list: List[Double] = List(1.0,2.0,3.0,4.0)
    val none = None

    case class Test()

    val test = Test()

    def f(x: Any) = x match {
        case _: Some[Test] => println("_ matched")
        case None => println("None matched")
    }

    f(list)
    f(none)
    f(test)
  }
}

尝试编译上面的代码会导致“擦除”编译时警告.

$>scalac Test.scala
    Test.scala:11: warning: non-variable type argument Test in type pattern
 Some[Test] is unchecked since it is eliminated by erasure
            case _: Some[Test] => println("_ matched")
                    ^
    one warning found

我读了这个备受推崇的Stackoverflow post,但我不明白这里的类型擦除.