PluginFactory

PluginFactory is a mixin module turns an including class into a factory for its derivatives, capable of searching for and loading them by name. This is useful when you have an abstract base class which defines an interface and basic functionality for a part of a larger system, and a collection of subclasses which implement the interface for different underlying functionality.

An example of where this might be useful is in a program which talks to a database. To avoid coupling it to a specific database, you use a Driver class which encapsulates your program’s interaction with the database behind a useful interface. Now you can create a concrete implementation of the Driver class for each kind of database you wish to talk to. If you make the base Driver class a PluginFactory, too, you can add new drivers simply by dropping them in a directory and using the Driver’s create method to instantiate them:

Synopsis

in driver.rb:

  require "PluginFactory"

  class Driver
        include PluginFactory
        def self::derivative_dirs
           ["drivers"]
        end
  end

in drivers/mysql.rb:

  require 'driver'

  class MysqlDriver < Driver
        ...implementation...
  end

in /usr/lib/ruby/1.8/PostgresDriver.rb:

  require 'driver'

  class PostgresDriver < Driver
        ...implementation...
  end

elsewhere

  require 'driver'

  config[:driver_type] #=> "mysql"
  driver = Driver.create( config[:driver_type] )
  driver.class #=> MysqlDriver
  pgdriver = Driver.create( "PostGresDriver" )