Why can't Scala optimize this match to a switch?

Question

I have this pattern match that matches only on Byte values but when I add the @switch it says:

could not emit switch to @switch annotated match

What am I missing here?

Just FYI, what I have tried already and did not work:

• Moving this constant to a Java interface and using public static final byte fields (I have also tried making them int instead of byte)
• Marking the fields as final val at the Scala Message companion object
• Marking the fields as @inline at the companion object

I'm definitely lost here.

Answer 1

The answer as provided at the scala-user forum was making the vals final and removing the Byte annotation:

object Message {
  final val Authentication = 'R'
  final val BackendKeyData = 'K'
  final val Bind = 'B'
  final val BindComplete = '2'
}

Now the @switch correctly generates a lookupswitch (it doesn't generate a tableswitch but it's good enough).