From: Paul Smith <paul@...>
Date: 2009-09-18T00:28:25+09:00
Subject: Re: Mucking about with dynamically adding methods to objects

2009/9/17 Jesús Gabriel y Galán <jgabrielygalan@gmail.com>:
> 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,
>

Thanks

I think I have a lot more reading to do before

irb(main):014:2> (class << obj;self;end).instance_eval do
irb(main):015:3* define_method :talk do

makes any kind of sense.
-- 
Paul Smith
http://www.nomadicfun.co.uk

paul@pollyandpaul.co.uk