From: John Lam <drjflam@...>
Date: 2006-05-13T02:44:08+09:00
Subject: Re: Inheriting class-based state

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Thanks, Joel - this is exactly what I needed to fix some ugliness in
RubyCLR.

I was trying to get class variables to work earlier, and actually ran acros=
s
the problem that you mentioned in your (*). I just didn't know it at the
time :)

Cheers,
-John
http://www.iunknown.com


On 5/12/06, Joel VanderWerf <vjoel@path.berkeley.edu> wrote:
>
> An alternative:
>
> class A
>   class << self
>     attr_accessor :__my_name
>
>     def my_name; A.__my_name; end
>     def my_name=3D(n); A.__my_name =3D n; end
>   end
> end
>
> class B < A
> end
>
> B.my_name =3D "fred"
>
> p A.my_name  # =3D=3D> "fred"
>
> Or, if you don't want __my_name polluting the namespace, you could use
> this:
>
> class A
>   class << self
>     def my_name; A.instance_variable_get(:@my_name); end
>     def my_name=3D(n); A.instance_variable_set(:@my_name, n); end
>   end
> end
>
> class B < A
> end
>
> B.my_name =3D "fred"
>
> p A.my_name
>
> The key difference between these two examples and your original attempt
> is that, here, the "A" reference binds _statically_ to the class A,
> whereas, in the original code, the "@my_name" reference binds
> _dynamically_ to the instance on which my_name is called (which might
> turn out to be A, or B or ...).
>
> HTH.
>
>

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