Failing to match on singleton type

I have no preliminary knowledge in this, but here are some clues :

> object W
defined module W

> (Some(W): Option[_ >: W.type]) match {
> case Some(W) => "yo"
> case None => "no"
> }
res21: java.lang.String = yo

also :

> class A
defined class A

> object B extends A
defined module B

> (Some(B): Option[A]) match {case Some(B) => "yo"; case None => "no"}
res14: java.lang.String = yo

What I suspect is that B.type is an artificial type only meant for
reflection, and that doesn't appear in the type hierarchy of your
program, from the compiler point of view.
B.isInstanceOf[B.type] will yield true. Some compiler magic for
reflection purposes ? Maybe structural types are involved ?

Waiting for the big shots to answer here :).

Alex

2012/1/25, Chris Marshall :
>
> Reported:
> https://issues.scala-lang.org/browse/SI-5406
>
> From: oxbow_lakes [at] hotmail [dot] com
> To: scala-user [at] googlegroups [dot] com
> Subject: [scala-user] Failing to match on singleton type
> Date: Tue, 24 Jan 2012 11:02:55 +0000
>
>
>
>
>
>
>
> This is using 2.9.1 - I can't find any matching issues
> scala> object Wufflesdefined module Wuffles
> scala> (Some(Wuffles): Option[Wuffles.type]) match { case Some(Wuffles) =>
> println("Woof"); case _ => println("Meow") }:10: error: pattern
> type is incompatible with expected type; found : object Wuffles required:
> Wuffles.type (Some(Wuffles): Option[Wuffles.type]) match { case
> Some(Wuffles) => println("Woof"); case _ => println("Meow") }
> ^
> The complaint is seems to be that Wuffles is not of Wuffles.type
> scala> Wufflesres10: Wuffles.type = Wuffles$@11dc088
> OK. Is this a new bug, a bug I can't find in JIRA, or a feature? Seems to be
> fixable by:
> scala> (Some(Wuffles): Option[Wuffles.type]) match { case Some(wuffles:
> Wuffles.type) => println("Woof"); case _ => println("Meow") }Woof
>
> Chris