configuration_example_v2.rb

require 'singleton'

# The gem's main module.
module AwesomeGem
  # A class method which yields the configuration to a block.
  def self.configure
    yield Configuration.instance if block_given?
    # Call all the registered listeners after configuration has taken place!
    Configuration.instance.listeners.each { |listener| listener.call }
  end

  # A class method to access the configuration instance.
  def self.configuration
    Configuration.instance
  end
  
  # The event to listen to.
  def self.on_configure(&block)
    # Add the passed block to the list of listeners.
    Configuration.instance.add_listener block
  end

  # Our gem's configuration class, includin Ruby's singleton model.
  class Configuration
    include Singleton

    # The list of configuration options our module will have.
    CONFIG_OPTIONS = [:do_magic, :awesome_string]

    attr_writer(*CONFIG_OPTIONS)
    
    # Add a lambda to the list of listeners.
    def add_listener(listener_lambda)
      @listeners << listener_lambda
    end

    def listeners
      @listeners
    end

    # Accessor methods for the options.
    def do_magic?
      @do_magic 
    end

    def awesome_string
      @awesome_string
    end
  end
end