SuperModule   SuperModule 2 Beta

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Calling Ruby's Module#include to mix in a module does not bring in class methods by default. This can come as quite the surprise when attempting to include class methods via a module.

Ruby offers one workaround in the form of implementing the hook method Module.included(base) following a certain boilerplate code idiom. Unfortunately, it hinders code maintainability and productivity with extra unnecessary complexity, especially in production-environment projects employing many mixins (e.g. modeling business domain models with composable object traits).

Another workaround is ActiveSupport::Concern, a Rails library that attempts to ease some of the boilerplate pain by offering a DSL layer on top of Module.included(base). Unfortunately, while it helps improve readability a bit, it adds even more boilerplate idiom cruft, thus feeling no more than putting a band-aid on the problem.

But do not fear, SuperModule comes to the rescue! By declaring your module as a super_module, it will simply behave as one would expect and automatically include class methods along with instance methods, without any further work needed.

Introductory Comparison

To introduce SuperModule, here is a comparison of three different approaches for writing a UserIdentifiable module, which includes ActiveModel::Model module as an in-memory alternative to ActiveRecord::Base superclass (Side-note: ActiveModel::Model is not needed when extending ActiveRecord::Base to connect to database.)

1) self.included(base)

module UserIdentifiable
  include ActiveModel::Model

  def self.included(base)
    base.extend(ClassMethods)
    base.class_eval do
      belongs_to :user
      validates :user_id, presence: true
    end
  end

  module ClassMethods
    def most_active_user
      User.find_by_id(select('count(id) as head_count, user_id').group('user_id').order('count(id) desc').first.user_id)
    end
  end

  def slug
    "#{self.class.name}_#{user_id}"
  end
end

This is a lot to think about and process for simply wanting inclusion of class method definitions (like most_active_user) and class method invocations (like belongs_to and validates). The unnecessary complexity gets in the way of problem-solving; slows down productivity with repetitive boiler-plate code; and breaks expectations set in other similar object-oriented languages, discouraging companies from including Ruby in a polyglot stack, such as Groupon's Rails/JVM/Node.js stack and SoundCloud's JRuby/Scala/Clojure stack.

2) ActiveSupport::Concern

module UserIdentifiable
  extend ActiveSupport::Concern
  include ActiveModel::Model

  included do
    belongs_to :user
    validates :user_id, presence: true
  end

  module ClassMethods
    def most_active_user
      User.find_by_id(select('count(id) as head_count, user_id').group('user_id').order('count(id) desc').first.user_id)
    end
  end

  def slug
    "#{self.class.name}_#{user_id}"
  end
end

A step forward that addresses the boiler-plate repetitive code concern, but is otherwise really just lipstick on a pig. To explain more, developer problem solving and creativity flow is still disrupted by having to think about the lower-level mechanism of running code on inclusion (using included) and structuring class methods in an extra sub-module (ClassMethods) instead of simply declaring class methods like they normally would in Ruby and staying focused on the task at hand.

3) SuperModule

super_module :UserIdentifiable do
  include ActiveModel::Model

  belongs_to :user
  validates :user_id, presence: true

  def self.most_active_user
    User.find_by_id(select('count(id) as head_count, user_id').group('user_id').order('count(id) desc').first.user_id)
  end

  def slug
    "#{self.class.name}_#{user_id}"
  end
end

Using super_module, developers can directly add class method invocations and definitions inside the module's body, and SuperModule takes care of automatically mixing them into classes that include the module.

As a result, SuperModule collapses the difference between extending a super class and including a super module, thus encouraging developers to write simpler code while making better Object-Oriented Design decisions.

In other words, SuperModule furthers Ruby's goal of making programmers happy.

By the way, SuperModule 2 Beta supports an alternate syntax as well:

UserIdentifiable = super_module do
end

Instructions

1) Install and require gem

Using Bundler

Add the following to Gemfile: 

gem 'super_module', '1.2.2'

And run the following command: 

bundle

Afterwards, SuperModule will automatically get required in the application (e.g. a Rails application) and be ready for use.

Using RubyGem Directly

Run the following command: 

gem install super_module

(add --no-ri --no-rdoc if you wish to skip downloading documentation for a faster install)

Add the following at the top of your Ruby file: 

require 'super_module'

2) Call super_module(name) and pass it the super module body in a block

super_module :UserIdentifiable do
  include ActiveModel::Model

  belongs_to :user
  validates :user_id, presence: true

  def self.most_active_user
    User.find_by_id(select('count(id) as head_count, user_id').group('user_id').order('count(id) desc').first.user_id)
  end

  def slug
    "#{self.class.name}_#{user_id}"
  end
end

3) Mix newly defined module into a class or another super module

class ClubParticipation < ActiveRecord::Base
  include UserIdentifiable
end
class CourseEnrollment < ActiveRecord::Base
  include UserIdentifiable
end
super_module :Accountable do
  include UserIdentifiable
end
class Activity < ActiveRecord::Base
  include Accountable
end

4) Start using by invoking class methods or instance methods

CourseEnrollment.most_active_user
ClubParticipation.most_active_user
Activity.last.slug
ClubParticipation.create(club_id: club.id, user_id: user.id).slug
CourseEnrollment.new(course_id: course.id).valid?

Glossary and Definitions

  • SuperModule: name of the library and Ruby module that provides functionality via mixin
  • Super module: any Ruby module that mixes in SuperModule
  • Singleton class: also known as the metaclass or eigenclass, it is the object-instance-associated class copy available to every object in Ruby (e.g. every Object.new instance has a singleton class that is a copy of the Object class, which can house instance-specific behavior if needed)
  • Singleton method: an instance method defined on an object's singleton class. Often used to refer to a class or module method defined on the Ruby class object or module object singleton class via def self.method_name(...) or class << self enclosing def method_name(...)
  • Class method invocation: Inherited Ruby class or module method invoked in the body of a class or module (e.g. validates :username, presence: true)
  • Code-time: Time of writing code in a Ruby file as opposed to Run-time
  • Run-time: Time of executing Ruby code

Usage Details

  • SuperModule must always be included at the top of a module's body at code-time
  • SuperModule inclusion can be optionally followed by other basic or super module inclusions
  • A super module can only be included in a class or another super module
  • SuperModule adds zero cost to instantiation of including classes and invocation of included methods (both class and instance)

IRB Example

Create a ruby file called super_module_irb_example.rb with the following content:

require 'rubygems' # to be backwards compatible with Ruby 1.8.7
require 'super_module'

super_module :RequiresAttributes do

  def self.requires(*attributes)
    attributes.each {|attribute| required_attributes << attribute}
  end

  def self.required_attributes
    @required_attributes ||= []
  end

  def requirements_satisfied?
    !!self.class.required_attributes.reduce(true) { |result, required_attribute| result && send(required_attribute) }
  end
end

class MediaAuthorization
  include RequiresAttributes
  attr_accessor :user_id, :credit_card_id
  requires :user_id, :credit_card_id
end

Open irb (Interactive Ruby) and paste the following code snippets in. You should get the output denoted by the rockets (=>).

require './super_module_irb_example.rb'

=> true

MediaAuthorization.required_attributes

=> [:user_id, :credit_card_id]

media_authorization = MediaAuthorization.new # resulting object print-out varies

=> #MediaAuthorization:0x832b36be1

media_authorization.requirements_satisfied?

=> false

media_authorization.user_id = 387

=> 387

media_authorization.requirements_satisfied?

=> false

media_authorization.credit_card_id = 37

=> 37

media_authorization.requirements_satisfied?

=> true

How Does It Work?

V2 has a much simpler algorithm than V1 that goes as follows:

  1. Handle invocation of super_module(name, &super_module_body) method anywhere in the Ruby code where the block it receives represents the super module body, including instance methods, and class methods, and class body invocations.
  2. Clone SuperModule and store in it the passed in super_module_body block
  3. Assign the cloned SuperModule to a new constant as defined by name (e.g. 'Utilities::Printer') under a class, module, or the top-level Ruby scope
  4. When calling include on the module later on, its stored super_module_body attribute is retrieved and run in the including class or module body via class_eval

Limitations and Caveats

  • SuperModule has been designed to be used only in the initial code definition of a module (not supporting later re-opening of the module.)

  • Given SuperModule's implementation relies on self.included(base), if an including super module (or a super module including another super module) must hook into self.included(base) for meta-programming cases that require it, such as conditional include statements or method definitions, it would have to alias self.included(base) and then invoke the aliased version in every super module that needs it like in this example:

    super_module :AdminIdentifiable do
include UserIdentifiable

class << self
    alias included_super_module included
    def included(base)
        included_super_module(base)
        # do some extra work
        # like conditional inclusion of other modules
        # or conditional definition of methods
    end
end
end

    In the future, SuperModule could perhaps provide robust built-in facilities for allowing super modules to easily hook into self.included(base) without interfering with SuperModule behavior.

What's New?

v2 Beta (v1.2.2)

  • Relaxed dependency on method_source gem version

v2 Beta (v1.2.1)

  • Standalone super module usage (e.g. direct class method invocation)

v2 Beta (v1.2.0)

  • New super_module(name) syntax
  • Much simpler implementation with guaranteed correctness and no performance hit
  • Less memory footprint by not requiring method_source Ruby gem for v2 syntax
  • Backwards compatibility with v1 syntax

v1.1.1

  • Added support for private and protected methods
  • Added many more RSpec test cases, including testing of empty and comment containing singleton methods

v1.1.0

  • Brand new self-friendly algorithm that ensures true mixing of super module singleton methods into the including base class or module, thus always returning the actual base class or module self when invoking a super module inherited singleton method (thanks to Banister for reporting previous limitation on Reddit and providing suggestions)
  • New included_super_modules inherited singleton method that provides developer with a list of all included super modules similar to the Ruby included_modules method.
  • No more use for method_missing (Thanks to Marc-AndrĂ© Lafortune for bringing up as a previous limitation in AirPair article reviews)
  • New dependency on Banister's method_source library to have the self-friendly algorithm eval inherited class method sources into the including base class or module.
  • Refactorings, including break-up of the original SuperModule into 3 modules in separate files
  • More RSpec test coverage, including additional method definition scenarios, such as when adding dynamically via class_eval and define_method

Feedback and Contribution

SuperModule is written in a very clean and maintainable test-first approach, so you are welcome to read through the code on GitHub for more in-depth details: https://github.com/AndyObtiva/super_module

The library is quite new and can use all the feedback and help it can get. So, please do not hesitate to add comments if you have any, and please fork the project on GitHub in order to make contributions via Pull Requests.

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Copyright (c) 2014-2016 Andy Maleh. See LICENSE.txt for further details.