From: Enrique Comba Riepenhausen <ecomba@...>
Date: 2007-05-12T00:17:45+09:00
Subject: Re: Is there a possibility to include methods of a class?


On 11 May 2007, at 17:14, Brian Candler wrote:

> On Fri, May 11, 2007 at 10:29:01PM +0900, Bernd wrote:
>> Hi all,
>> first of all: this list and you rock! I know that there is no  
>> multiple
>> inheritance, but you can use the concept of mixin.
>> However, I want to inherit my class another and "mixin" methods from
>> another class.
>> To be more precise,
>> I have a class that inherits another one (that comes from a  
>> library and
>> I do not want to change) and I want the methods of  
>> ActiveRecord::Base in
>> my class. Is there a way to do that (without copying and paste the  
>> whole
>> ActiveRecord::Base class and changing it to a module)?
>
> I would use delegation for one class or the other.
>
> That is: define your class as
>
> class Foo < ActiveRecord::Base
>   ..
>   def initialize
>     @other = Library::Bar.new
>   end
> end
>
> Or vice versa, whichever makes more sense. And if you can't choose,  
> then
> delegate to both.
>
> class FooDB < ActiveRecord::Base
>   .. more stuff
> end
>
> class Foo
>   def initialize(id)
>     @db = FooDB.find(id)
>     @lib = Library::Bar.new
>   end
> end
>
> Then the interface that Foo exposes to the world can pass some  
> calls to @db,
> some to @lib, or (the best news) can combine behaviours from both in
> whichever way it likes.
>
That would actually be a so called Bridge Design Pattern... I like it  
I think I will use it for Ruby Patterns ;)

Thanks Brian!