From: "Kurt M. Dresner" <kdresner@...>
Date: 2003-08-22T15:57:03+09:00
Subject: Re: Class variables - a surprising result

That is a really good way to think about it.  I think I like the way
that the @@class variables work now.

:o)

-Kurt

On Fri, Aug 22, 2003 at 02:19:12PM +0900, Ryan Pavlik wrote:
> On Fri, 22 Aug 2003 13:59:54 +0900
> Patrick Bennett <patrick.bennett@inin.com> wrote:
> 
> > Dan Doel wrote:
> <snip>
> > > Foo.print # => 6
> > > Foo.new.print # => nil 
> > 
> > Geesh - sneaky stuff..  This kind of thing *definitely* violates the 
> > P.O.L.S. imo.  For one, having the 'same' variable actually be two 
> > different 'instances' (one, a class variable effectively,
> > and another, an instance variable) is very confusing.  I understand it 
> > now (although I have to think about it for a sec, and personally, I 
> > think that's a bad sign).
> > I think the above @var=6 assignment outside of a method decl should be 
> > illegal.  It should have to be a @@ reference.
> 
> 
> Definitely not.  One of the coolest things about ruby is that when you
> say "class" or "module", it doesn't open a declarative section of code,
> but rather an new executive section.   This helps greatly in eliminating
> special syntaxes.  For instance:
> 
>     class A
>         attr_accessor :a, :b
> 
>         private
> 
>         def foo; ... end
>     end
> 
> In this case, "attr_accessor" and "private", which would regularly be
> syntax, are actually method calls.  This is Very Cool:
> 
>     class Module
>       def def_abstract(*args)
>         for sym in args
>           module_eval <<-CODE
>           def #{sym}(*args); raise SubclassResponsibility; end
>           CODE
>         end
>       end #m:def_abstract
>     end #c:Module
> 
> Now I can do:
> 
>     class B
>        def_abstract :foo, :bar
>     end
> 
> Nifty!  In fact, I've used this to define new attr_* functions, and a
> few other things, to make life easier:
> 
> 
>     class C
>         attr_accessor_typed String, :title, :text
>     end
> 
> The fact that a class or module body is just code along with everything
> else gives great flexibility.
> 
> As for @instance variables of Class being confusing... it's not at all.
> It's like this:
> 
>     #<Class D:0x1234 @a=42>  <--- Over here we have a Class object
> 
>        over here we have a D object ----->  #<D:0x4321 @x=0, @y=0>
> 
> If you think of everything being an object, the proper place to put your
> "static" variables is in the Class object itself.  It's a matter of
> understanding the proper way to think about Ruby, rather than trying to
> translate it into something else.
> 
> -- 
> Ryan Pavlik <rpav@users.sf.net>
> 
> "Let super-dimensional physics take its course!" - 8BT
> 
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