[scala] Strangeness with self types & wildcards in 2.8

[bearfeeder]

Howdy,

I've got a construct:

trait Frog[T] {

  def hello: T 

  def size: Int                                                                                                                                                          

}

trait OnlyWithFrogs {

  self: Frog[_] =>

    def sizeStr = size.toString

}

The OnlyWithFrogs trait must be mixed into a Frog (no, it's not okay to make it derive from Frog).  The above code worked with 2.7.5, but fails in 2.8 with:

: error: illegal cyclic reference involving type _$1

[WARNING]   self: Frog[_] =>

So, I tried to make my own wildcard:

  self: Frog[(Q forSome {type Q})] =>

This compiles, but when I try to create a concrete instance:

object Ribbit extends Frog[String] with OnlyWithFrogs {

  def hello = "Hi"

  def size = 44

}

The results in the following compile-time error:

[WARNING]  error: illegal inheritance;

[WARNING]  self-type net.liftweb.mapper.Ribbit.type does not conform to net.liftweb.mapper.OnlyWithFrogs's selftype net.liftweb.mapper.OnlyWithFrogs with net.liftweb.mapper.Frog[Q forSome { type Q }]

[WARNING] object Ribbit extends Frog[String] with OnlyWithFrogs {

Is this a bug in 2.8 worthy of a ticket or is there another way to deal with the wildcard/self-type issue?

Thanks,

David

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