From: Paul Smith <paul@...>
Date: 2009-09-17T18:44:16+09:00
Subject: Mucking about with dynamically adding methods to objects

I've been toying with Ruby for a while, but only now am I beginning to
understand some of the amazing properties Ruby has.  I was simply
floored when I realise you could add methods to an object dynamically.

So I saw this:

obj=Object.new

def obj.talk
  puts "Hello!"
end

and was stunned.  obj now has a talk method!

I took it to the next logical step, making a class which could add
methods to objects:

class FairyGodmother
  def talkify(obj)
    def obj.talk
      puts "I'm a real boy!"
    end
  end
end

fairy = FairyGodother.new()
pinocchio = Object.new()

fairy.talkify(pinochio)

pinochio.talk # Success!

But my next logical leap doesn't work:

Changing the talkify method to this:

def talkify(obj, str)
  def obj.talk
    puts str
  end
end

doesn't do what I mean - what it does is create a method called talk
which tries to output obj.str which doesn't exist.  What I want is for
the obj.talk method to return the literal string given to the
fairy.talkify call.

How do I convince Ruby to evaluate str?

(Apologies if this is answered somewhere in The Well Grounded Rubyist
- I haven't finished the book yet :) )
-- 
Paul Smith
http://www.nomadicfun.co.uk

paul@pollyandpaul.co.uk