From: Brian Candler <B.Candler@...>
Date: 2007-05-12T00:14:03+09:00
Subject: Re: Is there a possibility to include methods of a class?

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.