From: Hal Fulton <hal9000@...>
Date: 2004-01-15T06:40:07+09:00
Subject: Nested scopes and the Singleton pattern

Hello all,

This is really two questions.

I've been putting together a nested class structure in pieces
since it is a little large and unwieldy.

Here's a snippet of something I've run across.

By the way, my last change was to implement a simple version of the
Singleton pattern (without using singleton.rb).


   # Note: *Reopening* existing classes

   class ABC
     class XYZ
       @@instance = nil
       def initialize(foo)
         # Do some stuff...
         # and then:
         def XYZ.new(foo)
           @@instance
         end
       end
     end
   end


This works fine.

First question: Is this a valid way to implement Singleton, or am I
overlooking something?


Then I thought: Well, let's get rid of the unnecessary verbiage.
(Remember, I'm REOPENING these classes.)

So I did:

   # Note: *Reopening* existing classes

   class ABC::XYZ
     @@instance = nil
     def initialize(foo)
       # Do some stuff...
       # and then:
       def ABC::XYZ.new(foo)
         @@instance
       end
     end
   end

But it didn't work.

This does work:

   # Note: *Reopening* existing classes

   class ABC::XYZ
     @@instance = nil
     def initialize(foo)
       # Do some stuff...
       # and then:
       klass = ABC::XYZ
       def klass.new(foo)
         @@instance
       end
     end
   end


Second question: Why should these two be different?


Thanks,
Hal Fulton