From: "Jesús Gabriel y Galán" <jgabrielygalan@...>
Date: 2009-09-17T20:59:05+09:00
Subject: Re: Mucking about with dynamically adding methods to objects

On Thu, Sep 17, 2009 at 11:44 AM, Paul Smith <paul@pollyandpaul.co.uk> wrote:

> 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.

The problem here is that def starts a new scope, so str is undefined there.
This is a try with define_object instead:

irb(main):012:0> class A
irb(main):013:1> def talkify(obj,str)
irb(main):014:2> (class << obj;self;end).instance_eval do
irb(main):015:3* define_method :talk do
irb(main):016:4* puts str
irb(main):017:4> end
irb(main):018:3> end
irb(main):019:2> end
irb(main):020:1> end
=> nil
irb(main):021:0> o = Object.new
=> #<Object:0xb7d62cf4>
irb(main):023:0> A.new.talkify o,"hi"
=> #<Proc:0xb7d64f40@(irb):15>
irb(main):024:0> o.talk
hi
=> nil

We call define_method in the singleton class of obj. We need the
instance_eval because define_method is private.

Hope this helps,

Jesus.