From: David Alan Black <dblack@...>
Date: 2002-06-22T04:23:24+09:00
Subject: Re: Mixin using append_features and class<<self do not work together

Hello --

On Sat, 22 Jun 2002, Philipp Meier wrote:

> Hello to all,
>
> First, I'm new to ruby so please forgive if I read over the solution in
> the ruby doc or pickaxe book.

Welcome nuby!

> I'd like to know if it's possible to add a method to an object
> _instance_ at runtime? I tried sth. like instance_eval and "class <<
> self" which works. But do I add a mixin at runtime?
>
> I have a Mixin like this:
>
> Module B
>   def B.append_features(aClass)
>     def aClass.foo
>       "foo"
>     end
>   end
> end
>
> o = Object.new
> o.instance_eval<<-"end_eval"
>   include B
> end_eval
>
> But o.foo does not exist!?
>
> Is there a way to use append_features together with class<<self ?

See Bob's answer -- but also, I'm wondering whether there might be
simpler ways to do what you want to do.

For example, simplest case of adding a method to an object:

  o = Object.new
  def o.foo
    "foo"
  end

  p o.foo      # "foo"


Also, if you want to include a module in an object's metaclass:

  module B
    def foo
      "foo"
    end
  end

  o = Object.new
  class << o
    include B
  end

  p o.foo     # "foo"


Do you actually need #append_features for what you want to do?  (Not a
rhetorical question -- it is at least as likely that I am missing the
point as that my simplifications are appropriate :-)


David

-- 
David Alan Black
home: dblack@candle.superlink.net
work: blackdav@shu.edu
Web:  http://pirate.shu.edu/~blackdav