From: Trans <transfire@...>
Date: 2006-11-15T20:50:05+09:00
Subject: Re: Proc as Observer


Nobuyoshi Nakada wrote:
> Hi,
>
> At Wed, 15 Nov 2006 12:15:05 +0900,
> Trans wrote in [ruby-talk:225063]:
> > But your's doesn't work for immutables like NilClass. It's a a
> > bit more difficult in these cases. Have a clever solution? In any case
> > I'll take this and what I have and add it to Facets.
>
> Sorry, I'm not sure what you expect for NilClass.  Isn't this the
> case?
>
>   $ ./ruby -e 'nil.behaving(:foo){"Foo"}' -e 'p nil.foo'
>   "Foo"

My mistake. It is for Symbols that it doesn't work. I was mistakingly
thinking nil was the same, but that it not the case --which is great
b/c it makes my code obsolete! :-)

> > P.S. Would a cache on Behavior.new be a good optimization?
>
> It might be doubtful to be effective, since a Proc doesn't equal
> another Proc created in the same place almost.

Hmm... yes, I mean to go one step futher and catch the module and
create methods within it:

  class Behavior < Module
    def define(behavior, &body)
      if body
        define_method(behavior, &body)
      else
        behavior.each do |behavior, body|
          if body
            define_method(behavior, &body)
          elsif body.nil?
            remove_method(behavior)
          else
            undef_method(behavior)
          end
        end
      end
    end
  end

  module Kernel
    def behaving(behavior, &body)
      unless @_behaviors
        extend(@_behaviors ||= Behavior.new)
      end
      @_behaviors.define(behavior, &body)
    end
  end

T.