gistfile1.rb

class UserMigration < Migratrix::Migration
  set_extractor :mongo, :db => "funky"
end

class MongoExtractor
  def do_the_work
end

class Migratrix::Migration
  def self.mongo
    MongoExtractor.new
  end
end

Migratrix.register_extractor :mongo, MongoExtractor

class Migratix
  # basic method definition
  def self.register_extractor(key, klass)
    define_method(key) { klass.new }
  end

  def extract
    send(extractor_key).perform
  end

  # registry lookup
  def self.register_extractor(key, klass)
    registry[key] = klass
  end

  def extractor
    registry[extractor_key].new(extractor_options)
  end

  def extract
    extractor.perform
  end
end