From: "Hal E. Fulton" <hal9000@...>
Date: 2003-08-01T07:01:11+09:00
Subject: Re: Extracting a parent class

----- Original Message ----- 
From: "Michael Garriss" <mgarriss@earthlink.net>
To: "ruby-talk ML" <ruby-talk@ruby-lang.org>
Sent: Thursday, July 31, 2003 4:53 PM
Subject: Extracting a parent class


> Sorry about the newbie question but....
> 
> class A
>   attr_accessor :a
> end
> 
> class B < A
>   attr_accessor :b
> end
> 
> b = B.new
> b.a = "some data"
> b.b = "some more data"
> a = b.?????
> 
> How do I set 'a' from 'b' so that a is of class A and not class B?  I 
> don't want the extra info, I want just the subset of members found in 
> the parent class.  Is there a way to cast?

I don't know of a simple, direct way to do this.

Offhand it's possible that you're thinking in a 
C++ fashion and should simply do it another way.

You *could* add a class method for B that would
create an instance of A and return it...

  class B
    def B.to_A
      x = A.new
      x.a = self.a
      x
    end
  end

That's consistent with the ordinary principles of
an object knowing how to convert itself and a child
class having knowledge of a parent but not vice versa.

Hal


--
Hal Fulton
hal9000@hypermetrics.com