From: Rick DeNatale <rick.denatale@...>
Date: 2010-04-30T21:30:07+09:00
Subject: Re: Switching dynamically between methods (inside modules)

To me, this problem cries out for delegation rather than inheritance
or module inclusion.

Here's a first cut.

module Language

  Japanese = {
    :konnichiwa =>  "こんにちは！ (in  Japanese language)",
    :sayounara => "さようなら。 (in Japanese language)"
  }

  French = {
    :bonjour => "Bonjour ! (in French language)",
    :au_revoir => "Au revoir. (in French language)"
  }

  English = {
    :hello =>"Hello! (in English language)",
    :bye => "Bye. (in English language)"
  }

  class NewBornKnowledge
    def self.method_missing(word, *args)
      "Goo Goo Gaa Gaa (in BabyTalk)"
    end

    def to_s
      nil
    end
  end

  class Knowledge

    def initialize(language)
      @language = language
      @dictionary = Language.const_get(language.to_sym)
    end

    def to_s
      @language
    end

    def method_missing(word, *args)
      @dictionary[word] || "that's not a word in #{@language}"
    end

  end

  def self.knowledge_for(language=nil)
    if language
      Knowledge.new(language)
    else
      NewBornKnowledge
    end
  end

end

class Person
  def initialize(language = nil)
    self.current_language = language
  end

  def method_missing(word, *args)
    @language_center.send(word)
  end

  def current_language=(language)
    @language_center = Language.knowledge_for(language)
  end

  def quit
    self.current_language = nil
  end
end

person = Person.new

person.current_language # => "Goo Goo Gaa Gaa (in BabyTalk)"
person.hello            # => "Goo Goo Gaa Gaa (in BabyTalk)"

person.current_language = :English
person.hello    # => "Hello! (in English language)"
person.bonjour  # => "that's not a word in English"
person.quit

person.hello # => "Goo Goo Gaa Gaa (in BabyTalk)"
person.bonjour # => "Goo Goo Gaa Gaa (in BabyTalk)"
person.konnichiwa # => "Goo Goo Gaa Gaa (in BabyTalk)"

person.current_language = :French
person.bonjour  # => "Bonjour ! (in French language)"


This also has the advantage that it can fairly easily be extended to
support multilingual people.  Something even a few of us Americans
think is une bonne idée!

-- 
Rick DeNatale

Blog: http://talklikeaduck.denhaven2.com/
Github: http://github.com/rubyredrick
Twitter: @RickDeNatale
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