From: Ara.T.Howard@...
Date: 2005-04-30T09:54:28+09:00
Subject: Re: advice requested / attributes.rb

On Sat, 30 Apr 2005, Dave Burt wrote:

> I don't see that it's clear that these are not @@ variables - wouldn't that
> be the obvious implementation for that behaviour, and for something called
> "class attributes"?

if it WERE simply an @@var you'd have

   class A
     class_attribute 'x'
     x 42
   end

   class B < A
     x 42.0
   end

   p A::x #=> 42.0

but instead you get

   p A::x #=> 42
   p B::x #=> 42.0

if it were simply a class @var you'd have

   class A
     class_attribute 'x'
     x 42
   end

   class B < A
   end

   p B::x #=> nil

but instead you get

   p B::x #=> 42

and then if you

   class C < B; end

   B::x = 42.0

you'll have

   p A::x #=> 42
   p B::x #=> 42.0
   p C::x #=> 42.0

make sense?  you __inherit__ the 'x'.  with @vars every class has one and
there is no sharing.  with @@vars there is ONE and ONLY ONE - all classes in a
hierarchy share it.  this works using follow logic:

   - if you set the var you have it
   - else look up ancestry chain for it

cheers.

-a
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