From: "trans.  (T. Onoma)" <transami@...>
Date: 2005-01-17T23:22:30+09:00
Subject: Re: Fwd: [suby-ruby] Your all time desired fundemental Ruby mod

On Monday 17 January 2005 08:33 am, David A. Black wrote:
| Hi --
|
| On Mon, 17 Jan 2005, trans.  (T. Onoma) wrote:
| > On Monday 17 January 2005 02:51 am, Martin DeMello wrote:
| > | David A. Black <dblack@wobblini.net> wrote:
| > | > You're right -- I meant to clarify that I'm talking about 2.0 class
| > | > vars, which as I understand it will be truly per-class and will
| > | > differ from instance variables of Class objects principally in that
| > | > they will be in scope in instance methods.  I would rather not have a
| > | > separate construct that overlaps so much with instance variables.
| > |
| > | I can think of at least one good us for the current @@ variables -
| > | subclassable GUI components that inherit hierarchy-shared look-and-feel
| > | properties from the parent class. What would be the elegant way to do
| > | this if @@ variables go per-class?
| >
| > You would have to do it via class instance vars.
|
| They're per-class too :-)  You'd need accessor methods, I think.

Yes, of course: "via class instance thru via accessors" is waht I should have 
said.

| > The problem with these IMHO
| > is still the intialization issue, as with modules (see ruby-talk:121611,
| > http://urltron.com/nd) Matz, do you think we can get something in the way
| > of remedying that? For me it's one of the biggest sores in my code.
|
| I'm not sure I get what the problem is here.  In your examples you're
| overriding #initialize, and calling super to invoke the old one.
| That's pretty standard procedure -- it's what super is basically for,
| and it seems like the simplest design.  (I'm not sure what's supposed
| to happen in the future if instance vars become private to their
| module.)

Yes, true. But good SOC/ecapsulation meants that I should be able to modify a 
class with a module without having to adjust pre-existing parts of the class. 
For instance lets say I have class:

  class C
    def initialize
      @y = 11
    end
  end

I want to expand the functionality of this class with a module I have:

  module M
    def x ; @x ; end
  end

But @x needs to default to an array. So what do I do? Presently I have two 
choices. Either change M to:

  module M
    def x ; @x ||= [] ; end
  end

or use super as you suggest. But I don;t want to just recopy C for what if it 
changed internally later? So,

  module M
    def initialize
      @x = []
    end
    def x ; @x ; end
  end

  class C
    alias_method :init, :initialize
    def initialize(*args, &blk)
      super
      init
    end
  end

None of this is need though if we just had some way to "initialize_always".

Does that explain better?
T.