Welcome to Scala.next (pre-alpha, git-hash: unknown)  (OpenJDK 64-Bit Server VM, Java 1.8.0_131).
Type in expressions to have them evaluated.
Type :help for more information.
scala> class Ref[T] {
           private[this] var value: T = _

           def getValue(): T = value

           def setValue(v: T): Unit = {
                        println(s"setValue($v)")
                        value = v
                }
         }
defined class Ref
scala> def test(ref: Ref[_]) = ref.setValue(ref.getValue())
def test(ref: Ref[_]): Unit
scala> val ref1 = new Ref[Int]
val ref1: Ref[Int] = Ref@3a5c2626
scala> ref1.setValue(666)
setValue(666)
scala> test(ref1)
setValue(666)
scala> val refA: Ref[_] = new Ref[String]
val refA: Ref[_] = Ref@feb98ef
scala> val refB: Ref[_] = new Ref[Any]
val refB: Ref[_] = Ref@8cc8cdb
scala> refA.setValue(refA.getValue())
setValue(null)
scala> refA.setValue(refB.getValue())
-- [E007] Type Mismatch Error: <console>:8:27 ----------------------------------
8 |refA.setValue(refB.getValue())
  |              ^^^^^^^^^^^^^^^
  |              found:    refB.T
  |              required: refA.T
  |
scala> val refA2: refA.type = refA
val refA2: refA = Ref@feb98ef
scala> refA.setValue(refA2.getValue())
setValue(null)