Extend for class methods in Ruby - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the extend keyword do in Ruby?

It adds the methods from a module as class methods to the class or object it is called on.

beginner

How is extend different from include in Ruby?

<code>include</code> adds module methods as instance methods, while <code>extend</code> adds them as class methods.

beginner

Given <pre>module Greetings
  def hello
    "Hello!"
  end
end

class Person
  extend Greetings
end</pre> How do you call <code>hello</code>?

You call it on the class: Person.hello returns "Hello!".

intermediate

Can extend be used on individual objects in Ruby?

Yes, it adds the module's methods as singleton methods to that object only.

intermediate

Why use <code>extend</code> instead of defining class methods directly?

It promotes code reuse by sharing methods across classes without inheritance.

What does extend add to a Ruby class?

A Nothing, it just runs the module code

B Instance methods from a module

C Constants from a module

D Class methods from a module

extend adds module methods as class methods.

Which keyword adds module methods as instance methods in Ruby?

A require

B extend

C include

D import

include adds module methods as instance methods.

If a module has method foo, how do you call it after extend ModuleName in a class?

A ClassName.foo

B ClassName.new.foo

C ModuleName.foo

D You cannot call it

Methods added by extend become class methods.

Can extend be used on a single object instance?

A Yes, but adds methods to all instances

B Yes, adds methods only to that object

C No, only on classes

D No, it raises an error

extend can add methods to a single object as singleton methods.

What is a main benefit of using extend for class methods?

A Avoids code duplication by sharing methods

B Makes code run faster

C Changes instance variables

D Automatically creates instances

extend helps reuse code by sharing methods across classes.

Explain how extend works to add class methods in Ruby.

Think about where the methods become available after using extend.

Describe a scenario where using extend is better than inheritance.

Consider when you want to share behavior but classes don’t share a parent.