From: Robert Klemme <shortcutter@...>
Date: 2006-12-26T05:00:05+09:00
Subject: Re: class design

On 25.12.2006 20:54, Spitfire wrote:
>   How do I design a class such that it can never be instantiated? Say 
> for example a class containing static members alone, which requires no 
> instantiation!

You can apply some tactics to make it harder but AFAIK there is no safe 
way to completely prevent instantiation.  Typically something like this 
will suffice

class Foo
   def self.new(*a,&b) raise "Must not instantiate!" end
end

irb(main):004:0> Foo.new
RuntimeError: Must not instantiate!
         from (irb):2:in `new'
         from (irb):4
         from :0

Other than that you can also use module Singleton, which is probably 
better documentation wise:

irb(main):005:0> require 'singleton'
=> true
irb(main):006:0> class Bar
irb(main):007:1> include Singleton
irb(main):008:1> end
=> Bar
irb(main):009:0> Bar.new
NoMethodError: private method `new' called for Bar:Class
         from (irb):9
         from :0

Kind regards

	robert