how to use NSCoding with MacRuby

nscoding.rb

#!/usr/local/bin/macruby
framework 'Foundation'
class Note < NSObject
  attr_accessor :title, :author, :published
  def	initialize(title, author, published)
    self.conformsToProtocol(Protocol.protocolWithName('NSCoding'))
    @title, @author, @published = title, author, published
    # protocol NSCoding
  end
  def initWithCoder aDecoder
    @title = aDecoder.decodeObjectForKey "title"
    @author = aDecoder.decodeObjectForKey "author"
    @published = aDecoder.decodeBoolForKey "published"
    self
  end
  def encodeWithCoder anEncoder
    anEncoder.encodeObject @title, forKey:"title"
    anEncoder.encodeObject @author, forKey:"author"
    anEncoder.encodeBool @published, forKey:"published"
    self
  end
end

# create notes array
notes = []
articles = [{title:"Agora", author:“author1", published: true}, 
            {title:"thema", author:"author2", published: false},
            {title:"Topic", author:"Caren", published: true}]
articles.each do |note|
  notes << Note.new(note[:title],note[:author],note[:published])
end

# Given `notes` contains an array of Note objects
data = NSKeyedArchiver.archivedDataWithRootObject notes
NSUserDefaults.standardUserDefaults.setObject data, forKey:"notes"
p data

# Unarchiving is just as easy
notesData = NSUserDefaults.standardUserDefaults.objectForKey "notes"
notes = NSKeyedUnarchiver.unarchiveObjectWithData notesData
p notes