Factory pattern in Ruby

blog_post_importer.rb

class BlogPostImporter
  @@subclasses = { }
  def self.create type
    c = @@subclasses[type]
    if c
      c.new
    else
      raise "Bad importer type: #{type}"
    end
  end
  def self.register_importer name
    @@subclasses[name] = self
  end
end

def BlogPostImporter name, superclass=BlogPostImporter, &block
  Class.new(superclass, &block).register_importer(name)
end

imports_controller.rb

class Admin::ImportsController < Admin::BaseController
  def new
  end
  
  def create
    upload = params[:export_file]
    content = upload.is_a?(StringIO) ? upload.read : File.read(upload.local_path)
    
    importer_type = params[:import_type].parameterize.underscore.to_sym
    post_type     = params[:post_type].parameterize.underscore.to_sym
    date_type     = params[:post_date].parameterize.underscore.to_sym

    # load the blog post importer from the factory
    importer      = BlogPostImporter.create importer_type

    @result       = importer.import content, post_type, date_type
        
    flash[:notice] = @result
    
    redirect_to admin_path
  end
end

wordpress_importer.rb

require File.expand_path('../blog_post_importer', __FILE__)

require 'rexml/document'

BlogPostImporter :wordpress do
  def import(content, import_types = :all, date_type = :original)
    doc = REXML::Document.new(content)
    added = 0
    ignored = 0
    # loop through each post
    s = Time.now
    doc.elements.each('//item') do |ele|
      if ele.get_text("wp:post_type") == "post" || ele.get_text("wp:post_type") == "draft" # we only do posts
        draft = ele.get_text("wp:status") == "draft"

        should_save = (import_types == :all) || (import_types == :published && !draft) || (import_types == :draft && draft)

        if should_save
          make_post ele, date_type == :original
          added += 1
        else
          ignored += 1
        end
      end
    end
    bench = Time.now - s
    "#{added} posts were added to your blog, #{ignored} posts were skipped. It took #{bench} seconds."
  end

  def make_post(ele, use_original_date)
    @original_date = Date.parse(ele.get_text("wp:post_date").to_s)

    post = Post.new :title => ele.get_text("title").to_s,
                    :summary => ele.get_text("excerpt:encoded").to_s,
                    :body_html => ele.get_text("content:encoded").to_s

    post.created_at = @original_date if use_original_date

    post.save
  end
end