Extend for class methods in Ruby - Mini Project: Build & Apply

Extend a Module for Class Methods in Ruby

📖 Scenario: You are building a simple Ruby program to track books in a library. You want to add a feature that counts how many books have been created.

🎯 Goal: Create a module with a class method to count books. Then extend this module for class methods in the Book class.

📋 What You'll Learn

Create a module called BookCounter with a class method count that returns the number of books.

Create a class called Book.

Extend the BookCounter module for class methods in the Book class.

Create a class variable @@book_count in Book to track the number of books.

Increment @@book_count each time a new Book object is created.

Use the count class method to print the total number of books.

💡 Why This Matters

🌍 Real World

Counting objects like books, users, or orders is common in software to track totals or inventory.

💼 Career

Understanding how to add class methods via modules and track shared data is useful for Ruby developers building maintainable code.

1

Create the Book class with a class variable

Create a class called Book with a class variable @@book_count set to 0. Also, define an initialize method that increments @@book_count by 1 each time a new book is created.

Ruby

# Create the Book class with @@book_count and initialize method
# Your code here

Need a hint?

Use @@book_count to keep track of the number of books. Increment it inside initialize.

2

Create the BookCounter module with a class method

Create a module called BookCounter with a class method count that returns the value of @@book_count from the Book class.

Ruby

class Book
  @@book_count = 0

  def initialize
    @@book_count += 1
  end
end

# Create the BookCounter module with a class method count
# Your code here

Need a hint?

Use Book.class_variable_get(:@@book_count) inside the count method to access the class variable.

3

Extend BookCounter for class methods in Book

Extend the BookCounter module for class methods in the Book class using extend BookCounter.

Ruby

class Book
  @@book_count = 0

  def initialize
    @@book_count += 1
  end
end

module BookCounter
  def count
    Book.class_variable_get(:@@book_count)
  end
end

# Extend BookCounter module here
# Your code here

Need a hint?

Use Book.extend BookCounter after the class and module definitions to add class methods to Book.

4

Create books and print the total count

Create three Book objects named book1, book2, and book3. Then print the total number of books using Book.count.

Ruby

class Book
  @@book_count = 0

  def initialize
    @@book_count += 1
  end
end

module BookCounter
  def count
    Book.class_variable_get(:@@book_count)
  end
end

Book.extend BookCounter

# Create three Book objects and print the count
# Your code here

Need a hint?

Create three books with Book.new and print the count with puts Book.count.