Included hook in Ruby - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the included hook in Ruby modules?

The <code>included</code> hook runs automatically when a module is included in a class or another module. It allows you to add extra behavior or setup at the moment of inclusion.

beginner

How do you define an included hook inside a Ruby module?

You define a class method named <code>self.included(base)</code> inside the module. The <code>base</code> parameter is the class or module that includes this module.

intermediate

What can you do inside the included hook method?

Inside <code>included</code>, you can add methods, extend the including class with class methods, or perform setup tasks like adding callbacks or validations.

intermediate

Example: What will happen when this module is included?<br><pre>module Greetings
  def self.included(base)
    base.extend(ClassMethods)
  end

  module ClassMethods
    def say_hello
      "Hello!"
    end
  end
end

class Person
  include Greetings
end

Person.say_hello</pre>

The <code>included</code> hook extends the <code>Person</code> class with the <code>ClassMethods</code> module. So calling <code>Person.say_hello</code> will return <code>"Hello!"</code>.

intermediate

Why is the included hook useful compared to just including a module?

It lets you run extra code exactly when the module is included, like adding class methods or setting up behavior, which you can't do by just including instance methods.

What argument does the included hook method receive?

A The class or module that includes the module

B The name of the module being included

C No arguments are passed

D The instance of the including class

The included method receives the including class or module as an argument, allowing you to modify it.

Which keyword is used to define the included hook inside a module?

A def include_hook

B def included(base)

C def included!

D def self.included(base)

The included hook is defined as a class method with self.included(base).

What is a common use of the included hook?

A To define instance variables

B To delete methods from the including class

C To add class methods to the including class

D To create new modules

The included hook is often used to add class methods by extending the including class.

What happens if you include a module with an included hook in a class?

A The hook runs only when an instance is created

B The hook runs immediately during inclusion

C The hook never runs

D The hook runs when the class is defined

The included hook runs right when the module is included in the class.

Can the included hook be used to add instance methods to the including class?

A No, instance methods are added by the module itself

B Yes, but only if you call super

C Yes, by defining methods inside the hook

D No, it only adds class variables

Instance methods are added by the module itself; the included hook is mainly for extra setup like adding class methods.

Explain what the included hook does in Ruby modules and give an example of how it can be used.

Think about what happens when you include a module and want to add extra behavior.

Describe the difference between adding instance methods directly in a module and using the included hook to add class methods.

Consider what kinds of methods belong to instances vs the class itself.