This might be a known problem. The following code compiles in `dotc` and produces run-time exception. Scalac compiler rejects the code. ```Scala class Box[T](var v: T) object Test { def main(args: Array[String]): Unit = { val s = new Box[String]("") val i = new Box[Int](3) var box: Box[_] = s val sv = box.v box = i box.v = sv val c: Int = i.v } } ```