From: Dave Thomas <Dave@...>
Date: 2001-09-04T02:13:30+09:00
Subject: [ruby-talk:20791] Re: singleton help

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?

> 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.

   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