From: Michal Kwiatkowski <constant.beta@...>
Date: 2006-12-24T13:25:07+09:00
Subject: Re: Reverting module changes

dblack@wobblini.net wrote:
> I like to avoid the string version of module_eval (and similar), and
> use the block version instead, where possible.  To do that with your
> code, you could do:
>
> def system_should_return(what)
>    Kernel.module_eval do
>      alias_method :orig_system, :system
>      define_method(:system) {|*args| what.inspect }
>    end
> end
>
> def restore_system_behaviour
>    Kernel.module_eval do
>      alias_method :system, :orig_system
>    end
> end

I've tried to make a more versatile version of this that works for any
module and method. I've ended up with the following code:

class Module
  class Stub
    def initialize procedure
      @procedure = procedure
    end

    def and_return value
      @procedure.call value
    end
  end

  def override! method
    Stub.new(lambda do |value|
      alias_method(("orig_" + method.to_s).to_sym, method)
      define_method(method) { value }
    end)
  end

  def restore! method
    alias_method(method, ("orig_" + method.to_s).to_sym)
  end
end

With this code, to override the system method you can write (syntax
inspired by RSpec):

    Kernel.override!(:system).and_return false

and then to restore:

    Kernel.restore! :system

Can you suggest any improvements to this code?

> Note also that there's a library, available via RAA, that lets you do
> temporary changes to core behaviors:
>
> http://raa.ruby-lang.org/project/import_module/

Wow, very cool. Thanks!

Cheers,
mk