From: Robert Dober <robert.dober@...>
Date: 2008-06-12T19:22:37+09:00
Subject: Re: Class (not instance) Initializer

On Thu, Jun 12, 2008 at 12:50 AM, Greg Willits <lists@gregwillits.ws> wrote:
> Tim Hunter wrote:
>> Well, if you want to wait to do the initialization until the first
>> object is created, then something like this might work:
>>
>> def initialize
>>    populate_some_data if @@some_data == nil
>>    ...
>> end
>
> Duh. I should have figured that one out. Thanks.
>
> -- gw
>
> --
> Posted via http://www.ruby-forum.com/.
>
>


It is most unfortunate that class variables are still advocated so much :(.

The last but one line shows one of the problems of class variables,
they violate the principle that a base class shall never be touched by
the implementation of its subclasses - I know there is a classy name
for this but I forgot it ;)

--------------------------- 8< ---------------------------
203/79 > cat class_vars.rb && ruby class_vars.rb
# vim: sw=2 ts=2 ft=ruby expandtab tw=0 nu syn=on:
# file: class_vars.rb

class Base
  @@cvar=:Base
  @cinstvar=:base
  class << self
    attr_reader :cinstvar
    def cvar; @@cvar end
  end
end

class Sub < Base
  @@cvar = :Sub
  @cinstvar = :sub
end


puts "@@cvar in Sub: #{Sub.cvar}"
puts "@cinstaver in Sub: #{Sub.cinstvar}"
puts "==="*20
puts "@@cvar in Base: *****#{Base.cvar}******"
puts "@cinstaver in Base: #{Base.cinstvar}"


@@cvar in Sub: Sub
@cinstaver in Sub: sub
============================================================
@@cvar in Base: *****Sub******
@cinstaver in Base: base

--------------------------- 8< ------------------------------------


So the basic advice is to use Class instance variables, in your case
that might be written as

class Something
    @some_data = [1,2,3]
    class << self; attr_reader :some_data end
end

you can of course access them directly in class methods either defined
with the self idiom

  def self.print_data; puts @some_data end

or via the singleton class idiom

  class << self
       def print_data; puts @some_data end
  end

HTH
Robert





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---
As simple as possible, but not simpler.
Albert Einstein