From: David Alan Black <dblack@...>
Date: 2002-04-26T12:00:53+09:00
Subject: Re: how to check for unitialised class variable?

Hello --

On Fri, 26 Apr 2002, Ian Macdonald wrote:

> Hi,
>
> Observe the following:
>
> irb(main):006:0> class Foo
> irb(main):007:1>   def initialize
> irb(main):008:2>     @@foo ||= true
> irb(main):009:2>   end
> irb(main):010:1> end
> nil
> irb(main):011:0> bar = Foo.new
> NameError: uninitialized class variable @@foo in Foo
>         from (irb):8:in `initialize'
>         from (irb):11:in `new'
>         from (irb):11
>
> The ||= (only assign if nil) assignment operator must necessarily
> check for an existing value of @@foo and, if there isn't one, the
> above error ensues.
>
> How should one rewrite the above code? The objective is to avoid
> reassignment of @@foo, once it has been defined.

I think I'm on safe ground here, because I'm cutting-and-pasting
from ruby-talk:39007, by matz :-)  Adapt as appropriate:

  def MyClass
     unless defined? @@myClassVar
       @@myClassVar = nil
     end
  end


David

-- 
David Alan Black
home: dblack@candle.superlink.net
work: blackdav@shu.edu
Web:  http://pirate.shu.edu/~blackdav