x match {
case _: List[Int] => 1
case _: List[Char] => 2
case _: String => 3
}
This used java's semi-erased class tags and doesn't report a TypeTag constraint in its type. It will also return 1 when x is of type List[Char] since partial erasure means that the first two patterns end up being identical. The compiler will warn you about this situation, but generally it shows up all the time for various reasons. Super bad news.
That all said, the TypeTag system could be very nice someday. Especially if asInstanceOf were dropped eventually or, better, relied upon TypeTag.
That all said, the TypeTag system could be very nice someday. Especially if asInstanceOf were dropped eventually or, better, relied upon TypeTag.