From: Mauricio Fernandez <mfp@...>
Date: 2006-08-29T17:39:52+09:00
Subject: Re: Including a class.

On Tue, Aug 29, 2006 at 05:02:10PM +0900, Ola Bini wrote:
> As an extension on my earlier question of partial includes; I just 
> noticed that you can't include a Class, even though it is a Module.
> 
> Anyone have a way of doing this?
> 
> What I would like to do, is to be able to dynamically mix in some good 
> methods from preexisting classes, depending on arguments to the 
> constructor. Since I need to do it dynamically, and also need it 
> differently for different instances of the class, I can't make it 
> inherit the other class.
[...]

> But I can't have an instance of Bar or Foo so delegating is impossible. 
      ========================
> I need the methods to be in the the same instance. 

Doesn't this provide a very strong indication that you want to put the
reusable methods in modules? :-)

RUBY_VERSION                                 # => "1.8.5"
RUBY_RELEASE_DATE                            # => "2006-08-25"
module A; def foo; "A#foo" end end
module B; def foo; "B#foo" end end
class X; include A end
class Y; include B end
class Z
  def initialize(config = {})
    if config[:A]
      extend A
    elsif config[:B]
      extend B
    end
  end
end

Z.new(:A => true).foo                        # => "A#foo"
Z.new(:B => true).foo                        # => "B#foo"


[See [211308] for a Module#append_from implementation that doesn't clobber
inherited methods.]

-- 
Mauricio Fernandez  -   http://eigenclass.org   -  singular Ruby