From: dblack@...
Date: 2006-12-24T12:43:40+09:00
Subject: Re: Reverting module changes

Hi --

On Sun, 24 Dec 2006, Michal Kwiatkowski wrote:

> Mat Schaffer wrote:
>> On 12/23/06, Michal Kwiatkowski <constant.beta@gmail.com> wrote:
>>> I want to mock standard Kernel.system with my own method and then
>>> revert back to the original version. I was able to do the former, but
>>> not the latter. Currently I'm overwriting Kernel.system method
>>> definition with:
>>>
>>> def system_should_return what
>>>     Kernel.module_eval "def system(*args) #{what.inspect} end"
>>> end
>>>
>>> I don't a have idea how going back to the original state can be done.
>>> Thanks in advance for any help on this.
>>
>> Maybe there's something more elegant.  But I'd first alias the
>> original method, redefine it, then when I was done, I'd redefine it
>> again to just call the alias.
>
> Thanks, aliasing was what I was looking for. Does code below look OK or
> can be improved?
>
> def system_should_return what
>    Kernel.module_eval <<-EOV
>      alias_method :orig_system, :system
>      def system(*args)
>        #{what.inspect}
>      end
>    EOV
> end
>
> def restore_system_behaviour
>    Kernel.module_eval <<-EOV
>      def system()
>        orig_system
>      end
>    EOV
> end

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

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/

Actually there a couple of such libraries (including my Ruby
Behaviors), but that one is the most full-featured.  It might come in
handy if you do a lot of this or need thread safety.


David

-- 
Q. What's a good holiday present for the serious Rails developer?
A. RUBY FOR RAILS by David A. Black (http://www.manning.com/black)
    aka The Ruby book for Rails developers!
Q. Where can I get Ruby/Rails on-site training, consulting, coaching?
A. Ruby Power and Light, LLC (http://www.rubypal.com)