Ruby mixins and calling super methods

Question

Ok, so I've been refactoring my code in my little Rails app in an effort to remove duplication, and in general make my life easier (as I like an easy life). Part of this refactoring, has been to move code that's common to two of my models to a module that I can include where I need it.

So far, so good. Looks like it's going to work out, but I've just hit a problem that I'm not sure how to get around. The module (which I've called sendable), is just going to be the code that handles faxing, e-mailing, or printing a PDF of the document. So, for example, I have a purchase order, and I have Internal Sales Orders (imaginatively abbreviated to ISO).

The problem I've struck, is that I want some variables initialised (initialized for people who don't spell correctly :P ) after the object is loaded, so I've been using the after_initialize hook. No problem... until I start adding some more mixins.

The problem I have, is that I can have an after_initialize in any one of my mixins, so I need to include a super call at the start to make sure the other mixin after_initialize calls get called. Which is great, until I end up calling super and I get an error because there is no super to call.

Here's a little example, in case I haven't been confusing enough:

class Iso < ActiveRecord::Base
  include Shared::TracksSerialNumberExtension
  include Shared::OrderLines
  extend  Shared::Filtered
  include Sendable::Model

  validates_presence_of   :customer
  validates_associated    :lines

  owned_by                :customer
  order_lines             :despatched # Mixin

  tracks_serial_numbers   :items  # Mixin

  sendable :customer                      # Mixin

  attr_accessor :address

  def initialize( params = nil )
    super
    self.created_at ||= Time.now.to_date
  end
end

So, if each one of the mixins have an after_initialize call, with a super call, how can I stop that last super call from raising the error? How can I test that the super method exists before I call it?

Answer 1

You can use this:

super if defined?(super)

Here is an example:

class A
end

class B < A
  def t
    super if defined?(super)
    puts "Hi from B"
  end
end

B.new.t

Answer 2

Have you tried alias_method_chain? You can basically chained up all your after_initialize calls. It acts like a decorator: each new method adds a new layer of functionality and passes the control onto the "overridden" method to do the rest.