From: Albert Wagner <alwagner@...>
Date: 2001-09-04T10:47:40+09:00
Subject: [ruby-talk:20832] Re: singleton help

Hi, Dave.  Thanks for the reply.  It explains some bizarre behaviour I was 
getting :-)  But, a couple of follow-ups:

On Monday 03 September 2001 12:13, you wrote:
> Albert Wagner <alwagner@tcac.net> writes:
> > I need some help with a singleton class.
> >
> > 1.  With 'new' made private and replaced with 'instance',  how do I
> > properly pass in the arguments that would normally go to the
> > 'initialize(...)' method via 'new'?  Just use setter methods?
>
> There is a logical problem with having 'instance' take parameters
> (which is why is doesn't, I guess :). You could have
>
>    o1 = Fred.instance("barney")
>    o2 = Fred.instance("wilma")
>
> What would that mean?

Actually, I do need to pass an argument to the singleton.  It needs access to 
the class that created it (owner?)  I handled it with a setup(owner) method, 
but it seems inelegant.

>
> > 2.  If I subclass a singleton class, then create an instance of that
> > subclass, do I get the same instance with the additional behaviour of the
> > subclass?
>
> The subclass is it's own singleton: it doesn't share the singleton
> parent.

Great.  That works just as well.  As long as the subclassed singleton still 
inherits instance methods.

Thanks again.
>
>    class A
>      include Singleton
>    end
>    class B < A
>    end
>
>    a1 = A.instance
>    a2 = A.instance
>
>    b1 = B.instance
>    b2 = B.instance
>
> a1 and a2 will be the same, as will b1 and b2. a1 will not be the same
> as b1.
>
>
> Regards
>
>
> Dave