From: "David A. Black" <dblack@...>
Date: 2005-01-17T23:21:37+09:00
Subject: Re: Fwd: [suby-ruby] Your all time desired fundemental Ruby mod

Hi --

On Mon, 17 Jan 2005, trans.  (T. Onoma) wrote:

> On Monday 17 January 2005 08:20 am, David A. Black wrote:
> | Hi --
> |
> | On Mon, 17 Jan 2005, trans.  (T. Onoma) wrote:
> | > I generally agree with you. I wonder if @@vars could just become somesort
> | > of across the board initializer/accessor for instance vars (ie. @vars).
> | >
> | >  class C
> | >    @@a = 10
> | >    def a; @a; end
> | >  end
> | >  C.new.a  #=> 10
> |
> | Here you've got one object assigning to another object's instance
> | variables, which is not good.
>
> Except that class vars already do so in a sense in that they are accessable
> from both the class level and the instance level.

Class vars themselves have that scope, but they don't set instance
vars.

> But even so, that's not
> really what I meant. I'm actually with you on deprecating class vars, and was
> instead considering a completely alternate use for @@ notation to mean
> "default value of instance vars". This would address the issue in my other
> post about initialization of module's instance vars too, i.e.
>
>  module M
>    @@a = 10
>    def a; @a; end
>  end
>
>  class C
>    include M
>  end
>
>  C.new.a  #=> 10
>
> But maybe you already understood this and still find it not good?

Yes :-)  You've got one object (M) setting another object's instance
variables (those of C.new), without the owner-object's consent.  I
know that there are already things like instance_variable_set and so
on that can do this... but I personally take a pretty hard line on
instance variables being strictly the business of the instance whose
variables they are.  I don't think there should be a proliferation of
mechanisms for crossing that boundary.


David

-- 
David A. Black
dblack@wobblini.net