Module methods in Ruby - Mini Project: Build & Apply

Using Module Methods in Ruby

📖 Scenario: You are building a simple calculator program that can perform basic math operations. To keep the code organized, you will use a Ruby module to group the math methods.

🎯 Goal: Create a Ruby module named Calculator with methods for addition and subtraction. Then call these methods to perform calculations.

📋 What You'll Learn

Create a module named Calculator

Inside the module, define a method add that takes two numbers and returns their sum

Inside the module, define a method subtract that takes two numbers and returns their difference

Call the add and subtract methods from the Calculator module and print the results

💡 Why This Matters

🌍 Real World

Modules help organize related methods in Ruby programs, making code easier to maintain and reuse.

💼 Career

Understanding modules is important for Ruby developers to write clean, modular, and reusable code in real projects.

1

Create the Calculator module

Create a Ruby module called Calculator.

Ruby

# Create a module called Calculator
# Your code here

Hint

Use the keyword module followed by the module name and end to define a module.

2

Add methods to the Calculator module

Inside the Calculator module, define a method called add that takes two parameters a and b and returns their sum. Also define a method called subtract that takes two parameters a and b and returns their difference.

Ruby

module Calculator
  # Define add method
  # Your code here
  # Define subtract method
  # Your code here
end

Hint

Use def self.method_name to define module methods that can be called on the module itself.

3

Call the module methods

Call the add method from the Calculator module with arguments 10 and 5 and store the result in a variable called sum. Call the subtract method with arguments 10 and 5 and store the result in a variable called difference.

Ruby

module Calculator
  def self.add(a, b)
    a + b
  end

  def self.subtract(a, b)
    a - b
  end
end

# Call add and subtract methods
# Your code here

Hint

Call module methods using the module name followed by a dot and the method name.

4

Print the results

Print the values of sum and difference variables using two separate puts statements.

Ruby

module Calculator
  def self.add(a, b)
    a + b
  end

  def self.subtract(a, b)
    a - b
  end
end

sum = Calculator.add(10, 5)
difference = Calculator.subtract(10, 5)

# Print sum and difference
# Your code here

Hint

Use puts to print each variable on its own line.

Practice

1. What is the correct way to define a method inside a Ruby module so it can be called directly on the module?

easy

A. Define the method outside the module

B. Define the method without self inside the module

C. Define the method with self.method_name inside the module

D. Define the method with def module.method_name inside the module

Solution

1. Step 1: Understand module method definition

   In Ruby, to make a method callable directly on a module, you define it with self.method_name inside the module.

2. Step 2: Compare options

   Define the method with self.method_name inside the module uses self.method_name, which is correct. Other options either omit self or use invalid syntax.

3. Final Answer:

   Define the method with self.method_name inside the module -> Option C

4. Quick Check:

   Module methods use self.method_name = A [OK]

Hint: Use self.method_name to define module methods [OK]

Common Mistakes:

• Forgetting to add self before method name
• Defining methods outside the module
• Using invalid syntax like def module.method_name

2. Which of the following is the correct syntax to call a module method named greet defined in module Welcome?

easy

A. Welcome#greet

B. greet.Welcome

C. Welcome.new.greet

D. Welcome.greet

Solution

1. Step 1: Recall how to call module methods

   Module methods are called using dot notation: ModuleName.method_name.

2. Step 2: Check options

   Welcome.greet is the correct syntax using dot notation. Welcome#greet incorrectly uses #. greet.Welcome reverses the order. Welcome.new.greet confuses it with an instance method call.

3. Final Answer:

   Welcome.greet -> Option D

4. Quick Check:

   Call module methods with dot = D [OK]

Hint: Call module methods with ModuleName.method_name [OK]

Common Mistakes:

• Using # instead of . to call module methods
• Trying to call method with invalid syntax
• Confusing instance and module method calls

3. What will be the output of the following Ruby code?

module MathTools
  def self.square(x)
    x * x
  end
end

puts MathTools.square(4)

medium

A. 16

B. square

C. Error: undefined method

D. 4

Solution

1. Step 1: Understand the method definition

   The method square is defined as a module method using self.square. It returns the square of the input.

2. Step 2: Calculate the output

   Calling MathTools.square(4) returns 4 * 4 = 16, which is printed.

3. Final Answer:

   16 -> Option A

4. Quick Check:

   4 squared = 16 [OK]

Hint: Multiply input by itself in module method [OK]

Common Mistakes:

• Forgetting self and causing undefined method error
• Confusing output with input
• Expecting method name as output

4. Identify the error in this Ruby module method code:

module Greetings
  def greet
    "Hello!"
  end
end

puts Greetings.greet

medium

A. Method greet is not defined as a module method

B. Module name is incorrect

C. Missing parentheses in method call

D. Syntax error in method body

Solution

1. Step 1: Check method definition inside module

   The method greet is defined without self., so it is an instance method, not a module method.

2. Step 2: Understand method call

   Calling Greetings.greet tries to call a module method, but none exists, causing an error.

3. Final Answer:

   Method greet is not defined as a module method -> Option A

4. Quick Check:

   Missing self. means no module method [OK]

Hint: Add self. to define module methods [OK]

Common Mistakes:

• Defining instance methods instead of module methods
• Calling module method without defining it
• Assuming parentheses are required in method call

5. Given the module below, how can you add a module method double that returns twice the input number?

module Calculator
  # Add your method here
end

hard

A. def double(x)
x + x
end

B. def self.double(x)
x * 2
end

C. def Calculator.double(x)
x * 2
end

D. def self.double
x * 2
end

Solution

1. Step 1: Define a module method with self

   To create a module method, define it with self.method_name inside the module.

2. Step 2: Write method to return twice the input

   The method should take one argument x and return x * 2.

3. Final Answer:

   def self.double(x) x * 2 end -> Option B

4. Quick Check:

   Module method with self and correct logic = A [OK]

Hint: Use def self.method(args) for module methods [OK]

Common Mistakes:

• Omitting self and creating instance method
• Missing method argument
• Defining method outside module