From: Jason Bailey <azrael@...>
Date: 2005-02-24T02:22:37+09:00
Subject: Re: surprising: class A; end; A === A  ==> false

I'm thinking you can get what you want by

case t
when A.class then...
when B.class then...
end

since you want to compare the actual class of the object


> -------- Original Message --------
> Subject: surprising: class A; end; A === A  ==> false
> From: "Sam Roberts" <sroberts@uniserve.com>
> Date: Wed, February 23, 2005 11:24 am
> To: "ruby-talk ML" <ruby-talk@ruby-lang.org>
> 
> I'm used to thinking of === being MORE useful
> On thinking about it, I can see why: in A === A, A is of class Class,
> and that class is not derived from the class A, so comparison is
> false...
> 
> But this causes me some trouble, because there is no way to use
> case statements with a class:
> 
>   class A
>    Ordinal = 1
>   end
>   class B
>    Ordinal = 2
>   end
> 
>   t = A
> 
>   case t
>     when A then ...
>     when B then ...
>   end
> 
> No case will ever match!
> 
> Is my only way:
> 
>   if t == A
>     ...
>   elsif t == B
>     ...
>   elsif
>     .....
> 
> or is there some clever workaround?
> 
> I thought of
> 
>   t = A
> 
>   case t.new
>     when A then ...
> 
> 
> But in my case, A and B actually have initialize methods, and they
> require args (different args).
> 
> 
> Thanks,
> Sam
> 
> -- 
> Sam Roberts <sroberts@certicom.com>