From: Sean O'Halpin <sean.ohalpin@...>
Date: 2011-12-04T09:19:36+09:00
Subject: Re: Inverse Operation of Module#include

On Fri, Dec 2, 2011 at 6:57 AM, Su Zhang <su.comp.lang.ruby@gmail.com> wrote:
> Hi list,
>
> Is there a built-in inverse operation of Module#include? Currently I have:
>
[snip code]
>
> So if module B has already been mixed in, it cannot be re-included again
> thus the foo method is not redefined to B#foo in the last include operation.
> Thus occurs to me when I use Inversion of Control (or dependency injection)
> to switch between various implementations of a certain interface. I was
> thinking that if I can somehow "exclude" the module and include it again
> then the problem would be solved, and hence the question.
>
> Or better yet, is there another way to achieve this kind of implementation
> switching?
>
> Regards,
>
> Su
>

You could do this:

#!/usr/bin/env ruby
class A
end

module B
  def self.included(other)
    other.class_eval {
      def foo
        :b
      end
    }
  end
end

module C
  def self.included(other)
    other.class_eval {
      def foo
        :c
      end
    }
  end
end

a = A.new

class A
  include B
end
p a.foo # => :b

class A
  include C
end
p a.foo # => :c

class A
  include B
end
p a.foo # => :b

Regards,
Sean