From: Michael Garriss <mgarriss@...>
Date: 2003-08-01T07:13:31+09:00
Subject: Re: Extracting a parent class

It is VERY possible that I should be doing it in another way.  My 
motivation:  I have a client/server arch.  The server maintains objects 
and a database.  When the client needs something I do not want the 
client to have full access to all the info found in those server side 
objects.  Some of it would be bad for the client to know.  I have 
classes the client side can use and I add the additional things the 
server knows about the object by creating a subclass of the client class 
and then just adding the one or two 'secret' members.  Does this make sense?

Hal E. Fulton wrote:

>----- 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
>
>
>
>  
>