article_collection_proxy_class.rb

class Article
  attr_reader :filename

  def initialize(filename)
    @filename = filename
  end

  def <=> other
    self.filename <=> other.filename
  end

  def inspect
    %Q|#<Article filename="#{filename}">|
  end
end

class ArticleCollection
  include Enumerable

  def initialize(database)
    @database    = database                                          # <<< Implement
    @collection  = load_collection
  end

  def << item
    item = Article.new(item) unless item.is_a? Article
    @collection << item                                              # <<< Implement
    self
  end
  alias :add :<<

  def >> item
    item = item.filename if item.respond_to? :filename
    @collection.reject! { |a| a.filename == item }                   # <<< Implement
    self
  end
  alias :delete :>>

  def [] filename
    @collection.select  { |a| a.filename == filename }.first
  end
  alias :find :[]

  def <=> other
    self <=> other
  end

  def each(&block)
    @collection.each(&block)
  end

  private

  def load_collection                                                # <<< Implement
    []
  end

end

coll = ArticleCollection.new('articles') << Article.new('one') << Article.new('two')

puts "~~~ The collection..."
p coll

puts "~~~ Add 'three' and 'four'..."
coll << Article.new('three')
coll.add 'four'

p coll

puts "~~~ Deleting 'three' and 'four'..."
coll >> Article.new('three')
coll.delete 'four'

p coll

puts "~~~ Iteration..."
coll.each_with_index do |a, i|
  puts "#{i+1}. #{a.filename}"
end

puts "~~~ Mapping..."
p coll.map { |a| a.filename }

puts "~~~ Accessors..."
p coll['one']
p coll.find 'two'

puts "~~~ Count..."
p coll.count