From: Joel VanderWerf <vjoel@...>
Date: 2009-07-07T03:39:54+09:00
Subject: Re: A define_method question

Juston wrote:
> I have a question about define_method, more specifically how to bend
> it to my purpose.
> 
> The problem I am trying to solve is I have an object "Action" which
> basically carries out a static set of actions based off instance
> variables. "Action" can also be modified by MANY "Modifier"s. A
> "Modifier" just adds in a little bit of extra code that can changes an
> "Action"s operations just a bit. (Example: Action with a Modifier to
> email someone with a report, something I wouldn't want on every object
> and don't want to lump into some sort if/else statement in Action)
> 
> What I would like to be able to do is have an empty method
> "Action.runModifiedCode" within the "Action" class that would allow me
> to just inject the code right into "Action." This is easy enough to do
> using define_method (or a mix-in) to override the mock method, but
> this doesn't work when the "Action" has more than one "Modifier."
> 
> Long winded story short, is there something that would allow me to
> take the code from one object method and append to another object's
> method?

Are you sure mixins won't work?

class Action
   def do_stuff
     super if defined? super
     puts "starting to do stuff"
   end
end

module M1
   def do_stuff
     super if defined? super
     puts "M1 modifier"
   end
end

module M2
   def do_stuff
     super if defined? super
     puts "M2 modifier"
   end
end

module M3
   def do_stuff
     super if defined? super
     puts "M3 modifier"
   end
end

a = Action.new
a.extend M1
a.extend M2
class Action
   include M3 # M3 is global for all instances of Action
end

a.do_stuff
# ==>
# M3 modifier
# starting to do stuff
# M1 modifier
# M2 modifier

-- 
       vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407