From: Christopher Dicely <cmdicely@...>
Date: 2008-03-07T00:56:38+09:00
Subject: Re: Inheritance with Ruby

On Wed, Mar 5, 2008 at 4:19 PM, Chirag Patel <patelc75@yahoo.com> wrote:
> I would like to create a new superclass 'Super' for an existing class
>  'Sub'
>
>  class Sub
>   def new
>      #do something second
>   end
>  end
>
>  class Super < Sub
>   def new
>      #do something first
>   end
>  end

Note that this makes Sub a superclass of Super (Super inherits from
Sub), not the
other way around. I don't know if you can change the superclass of a class at
runtime, because Ruby uses single inheritance and Sub already has an parent
(Object). You can make a module, but AFAIK not a class even though a class is a
module, a "superclass" by including it.

>  Is it possible create this new Super class so that Super::new is called
>  every time Sub:new is called without modifying Sub?

No, but since Ruby has open classes, its pretty easy to modify sub so
that Super::initialize (what you probably really want) is called whenever
Sub::initialize is called (either before or after Sub::initialize executes).

>
>  The is because Sub already exists and I don't want to tamper the code.

You don't have to modify the code of that you are getting Sub from to
modify its behavior.

>  Basically I have a bunch of existing classes that I want to inherit from
>  'Super' so that I can include some error handling in 'Super'. Is there
>  another better way to accomplish this without modifying the existing
>  subclasses?

The best way is probably to create a module that does what you want,
and reopen the existing classes and include that module in each of them.