Extend for class methods in Ruby - Step-by-Step Execution

Concept Flow - Extend for class methods

Define Module with methods

↓

Create Class

↓

Extend Class with Module

↓

Call Module methods on Class

↓

Methods run as class methods

This flow shows how a module's methods become class methods when a class extends that module.

Execution Sample

Ruby

module Greetings
  def hello
    "Hello from class!"
  end
end

class Person
  extend Greetings
end

puts Person.hello

This code adds the module's method as a class method to Person and calls it.

Execution Table

Step	Action	Evaluation	Result
1	Define module Greetings with method hello	Module created	Module Greetings with method hello defined
2	Define class Person	Class created	Class Person defined
3	Extend Person with Greetings	Person gains module methods as class methods	Person.hello method available
4	Call Person.hello	Method runs	"Hello from class!" printed
5	End of program	No more code	Program ends

💡 Program ends after printing the class method result

Variable Tracker

Variable	Start	After extend	After method call	Final
Person	Class defined	Has class method hello	Method called	Class unchanged

Key Moments - 2 Insights

Why does Person.hello work after extend but not before?

Because extend adds module methods as class methods to Person, shown in step 3 of execution_table.

Is the hello method available to instances of Person?

No, extend adds methods only to the class itself, not its instances.

Visual Quiz - 3 Questions

Look at the execution_table, what happens at step 3?

A Person gains instance methods from Greetings

B Person loses all methods

C Person gains class methods from Greetings

D Greetings module is deleted

💡 Hint

See step 3 in execution_table where extend adds module methods as class methods

At which step is the method hello actually called?

A Step 4

B Step 3

C Step 2

D Step 5

💡 Hint

Step 4 shows calling Person.hello and printing the result

If we used include instead of extend, what would change?

A hello becomes a class method

B hello becomes an instance method

C hello is not added at all

D Program crashes

💡 Hint

Extend adds class methods; include adds instance methods

Concept Snapshot

Use extend to add module methods as class methods.
Syntax: class MyClass; extend MyModule; end
Methods in MyModule become callable on MyClass itself.
Unlike include, which adds instance methods.
Useful to share behavior at class level.

Full Transcript

This example shows how to use extend in Ruby to add methods from a module as class methods to a class. First, a module Greetings is defined with a method hello. Then, a class Person is defined. Using extend Greetings inside Person adds the hello method as a class method. When Person.hello is called, it runs the module method and prints the message. The execution table traces each step: defining the module, defining the class, extending the class, calling the method, and ending the program. The variable tracker shows Person gains the class method after extend. Key moments clarify that extend adds class methods, not instance methods. The quiz tests understanding of when methods are added and called, and the difference between extend and include. The snapshot summarizes the key points for quick reference.