gistfile1.rb

    def initialize (args={:event_time, :deadline, :event_name, :event_location, :minimum_attendees, :maximum_attendees, :creator_name, :phone, :email, :invitees})
      @required = args.fetch(:event_time, :deadline, :minimum_attendees) # .fetch will throw an error if key doesn't exist in Hash
      @optional = args[:creator, :event_name, :event_location, :attendees, :maximum_attendees] # simple access returns nil if key isn't set--no exception raised
    end

Example of putting optional parameters in the initialize method of a class.