From: David Alan Black <dblack@...>
Date: 2001-11-18T14:06:40+09:00
Subject: [ruby-talk:25741] Re: Parametric classes

Hello --

On Sun, 18 Nov 2001, Hal E. Fulton wrote:

> The confusing part is passing in the
> parent class to Class.new -- this is
> a parameter to the initialize method,
> but it's not used in my code.

What I think is happening is this:

When you do:

> Australian = Class.new(Nationality) do
>   @@native_lang = "English"
> end

Class.new handles the call, creating a class which is a child of
Nationality.  It then hands its arguments off to Class#initialize.  At
that point, #initialize does receive the parent argument, but doesn't
do anything with it (because its status as superclass has already been
assured by Class.new).

Is that what you were asking about, and is that explanation
reasonable?  (or even correct? :-)

> class Nationality
>
>   def Nationality.native_lang
>     class_eval("@@native_lang")
>   end
>
>   def Nationality.native_lang=(x)
>     class_eval("@@native_lang = #{x}")
>   end
>
>   #...
>
> end

That might be a good place for the idiom Guy D. was showing someone
earlier:

   class Nationality
     class << self
       attr_accessor :native_lang
     end
   end

which lets you use instance vars instead of class vars:

   Australian = Class.new(Nationality) do
     @native_lang = "English"
   end

(if that's appropriate for what you're doing).


David

-- 
David Alan Black
home: dblack@candle.superlink.net
work: blackdav@shu.edu
Web:  http://pirate.shu.edu/~blackdav