From: Logan Capaldo <logancapaldo@...>
Date: 2006-08-28T14:48:09+09:00
Subject: Re: Detecting when an object's instance variables are modifi


On Aug 27, 2006, at 5:37 PM, Paul Murton wrote:

> unknown wrote:
>> Hi --
>>
>> On Mon, 28 Aug 2006, David Vallner wrote:
>>
>>> monitor setters. Would probably be horribly, terribly slow.
>>>
>>> It's probably best to have your objects trace changes by design.  
>>> Modify the
>>> Object class to have a #dirty? and #clean! method, and alias /  
>>> redefine the
>>> #attr_writer method to generate methods that will set the dirty  
>>> flag when
>>> used?
>>
>> I was thinking of something similar, but using Observable -- but the
>> problem is that it would only work for instance variable changes that
>> go through attr_writer.
>>
>>
>> David
>
> I appreciate all of the help so far. I had considered the  
> possibility of
> redefining attr_writer, but had hoped there might be a way of doing  
> this
> so that it would work for changes that DON'T go through attr_writer.
>
> In fact this is actually quite important to me, because I am  
> interested
> in changes to ANY instance variable (including if a previously
> non-existant instance variable is set), not just those made externally
> accessible with a writer method. I should have been more clear about
> this in my original post.
>
> I've been thinking about this for ages now and my current thoughts are
> that there may not be any way of getting quite what I want here :/
>
> Any further suggestions appreciated
>

class A
   # all method definitions here
   ...

   instance_methods(false).each do |m|
     m_obj = instance_method(m)
     define_method(m) do |*args|
       before = instance_variables.inject({}) { |h,k| h[k] =  
instance_variable_get(k); h }
       res = m_obj.bind(self).call(*args)
       after =  instance_variables.inject({}) { |h,k| h[k] =  
instance_variable_get(k); h }
       return res
      end
   end
end

Salt and season to taste. (Note that the granularity is at the method  
level, not per statement, I'm assuming that's acceptable enough).

> -- 
> Posted via http://www.ruby-forum.com/.
>