From: Rick DeNatale <rick.denatale@...>
Date: 2009-11-15T01:39:00+09:00
Subject: Re: Surprising behavior when extending instances

On Sat, Nov 14, 2009 at 9:50 AM, Jim Crossley <jim@crossleys.org> wrote:
> This surprised me:
>
>  module English; def say; "yes"; end; end
>  module French; def say; "oui"; end; end
>  x = Object.new
>  x.extend English
>  x.say                 # "yes"
>  x.extend French
>  x.say                 # "oui"
>  x.extend English
>  x.say                 # "oui"
>
> What wrong assumptions am I making that this surprises me?

Matz has already explained that module inclusion is a one-time only deal.

Here's a bit on why that is.

http://talklikeaduck.denhaven2.com/2007/11/03/a-chat-with-matz-classs-variable-reversion-and-a-mystery-explained

>  What is
> the more elegant "Ruby way" of alternating an object's behavior at
> runtime?

I'd use a form of delegation

module English; def self.agree; "yes"; end; end
module French; def self.agree; "oui"; end; end

class Speaker

   attr_accessor :language

   def initialize(language = English)
      self.language = language
   end

   def say
       language.agree
   end

  def speak(language)
       self.language = language
  end
end

jack = Speaker.new
jacques = Speaker.new(French)

jack.say   # => "yes"
jacques.say # => "oui"

jack.speak(French)
jacques.speak(English)

jack.say   # => "oui"
jacques.say # => "yes"

jack.speak(English)
jacques.speak(French)

jack.say   # => "yes"
jacques.say # => "oui"





-- 
Rick DeNatale

Blog: http://talklikeaduck.denhaven2.com/
Twitter: http://twitter.com/RickDeNatale
WWR: http://www.workingwithrails.com/person/9021-rick-denatale
LinkedIn: http://www.linkedin.com/in/rickdenatale