case class Cell[A](var x: A)
object Test {
  def f1(x: Any)        = x match { case y @ Cell(_) => y } // Inferred type is Cell[Any]
  // def f2(x: Cell[_])    = x match { case y @ Cell(_) => y } // Inferred type is Cell[_]
  // def f3[A](x: Cell[A]) = x match { case y @ Cell(_) => y } // Inferred type is Cell[A]

  def main(args: Array[String]): Unit = {
    // val x = new Cell(1)
    // val y = f1(x)
    // y.x = "abc"
    // println(x.x + 1)
  }
}