From: "David A. Black" <dblack@...>
Date: 2009-11-30T06:24:11+09:00
Subject: Re: Class variables, instance variables, singleton; Ruby v. C++

Hi --

On Sat, 28 Nov 2009, Rick DeNatale wrote:

> As others have pointed out class variables are a pretty wonky area of
> Ruby.  In Ruby 1.8 if G is a actually a subclass of F, then whether or
> not @@x is the same instance variable for both depends in some cases
> on whether or not F got its instance variable before G did or not.
>
> When a class variable is initialized Ruby 1.8 looks through the chain
> of superclasses to see if a class variable with that name already
> exists, and if so uses that definition. If not it defines it for the
> current class.  Ruby 1.9 changed that so that now class variables are
> no longer shared with subclasses.

I think that was true briefly but not more recently:

$ irb191
irb(main):001:0> class C
irb(main):002:1>   @@x = 1
irb(main):003:1> end
=> 1
irb(main):004:0> class D < C
irb(main):005:1>   @@x = 2
irb(main):006:1> end
=> 2
irb(main):007:0> class C
irb(main):008:1>   @@x
irb(main):009:1> end
=> 2

(unless it's been re-reverted yet more recently and I haven't picked
up on it).


David

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