Methods In Enumeration Subtypes?

Hi,

I have this simple Enumeration:

object          Polarity
extends         Enumeration
{
   /** Negative */
   val neg = Value

   /** Ambipolar */
   val amb = Value

   /** Positive */
   val pos = Value
}


I'd like to define a unary inversion operator (~ or ! or some such) that
I can use like this:

   val pol: Polarity = ...
   val inv: Polarity = ~pol


The computation is trivial:

   def
   ~(pol: Polarity.Value): Polarity.Value =
       pol match {
           case neg => pos
           case amb => amb
           case pos => neg
       }


How can I define a method with this behavior that I can use as shown in
the "val inv..." definition above?


Randall Schulz

On Sunday March 22 2009, Naftoli Gugenheim wrote:
> I think def unary_~ = ...

Oh, sorry.

I was set straight by DRMacIver and others on #scala. The main problem
was that I was trying to define methods in an object derived from
Enumeration. I switched to using case objects instead with the unary
operator method defined in their shared base class.

Randall Schulz

You can switch back to Enumeration:

object Polarity extends Enumeration {

class V(s:String) extends Val(s) {
def unary_- = minus(this)
}

val pos = new V("pos")
val amb = new V("amb")
val neg = new V("neg")

private val minus = Map(pos->neg, amb->amb, neg->pos)
}

object Test extends Application {
import Polarity._

println(pos)
println(-pos)
}