a

scala> class A {
     |   case object O
     | }
defined class A

scala> val (x, y) = (new A, new A)
x: A = A@543e710e
y: A = A@57f23557

scala> x.O match { case y.O => 1; case x.O => 2 }
<console>:10: error: pattern type is incompatible with expected type;
 found   : y.O.type
 required: x.O.type
              x.O match { case y.O => 1; case x.O => 2 }
                                 ^

scala> x.O.asInstanceOf[Any] match { case y.O => 1; case x.O => 2 }
res2: Int = 2