Prepend for method chain insertion in Ruby - Mini Project: Build & Apply

Prepend for method chain insertion

📖 Scenario: Imagine you have a simple Ruby class that formats text messages. You want to add a new behavior that always adds a greeting at the start of the message, but you want to do this without changing the original class code directly.

🎯 Goal: You will learn how to use Ruby's prepend feature to insert a new method behavior at the start of an existing method chain. This lets you add a greeting before the original message is formatted.

📋 What You'll Learn

Create a class called MessageFormatter with a method format that returns a string.

Create a module called GreetingPrepender with a method format that adds a greeting before calling super.

Use prepend to insert GreetingPrepender into MessageFormatter.

Create an instance of MessageFormatter and call format to see the greeting added.

💡 Why This Matters

🌍 Real World

Using <code>prepend</code> helps developers add or change features in existing classes without editing their original code. This is useful in large projects or when using third-party libraries.

💼 Career

Understanding <code>prepend</code> is important for Ruby developers working on maintainable and extendable codebases, especially in frameworks like Rails where method chaining and module mixins are common.

1

Create the MessageFormatter class

Create a class called MessageFormatter with a method format that returns the string "This is the original message."

Ruby

# Create the MessageFormatter class with format method
# Your code here

Need a hint?

Define a class with class MessageFormatter and a method def format that returns the exact string.

2

Create the GreetingPrepender module

Create a module called GreetingPrepender with a method format that returns the string "Hello! " concatenated with super.

Ruby

class MessageFormatter
  def format
    "This is the original message."
  end
end

# Create the GreetingPrepender module with format method
# Your code here

Need a hint?

Define a module with module GreetingPrepender and a method format that adds "Hello! " before calling super.

3

Prepend the module to the class

Use prepend GreetingPrepender inside the MessageFormatter class to insert the module before the class methods.

Ruby

class MessageFormatter
  # Use prepend to insert GreetingPrepender
  # Your code here

  def format
    "This is the original message."
  end
end

module GreetingPrepender
  def format
    "Hello! " + super
  end
end

Need a hint?

Inside the class, write prepend GreetingPrepender before the method definitions.

4

Create instance and print formatted message

Create an instance of MessageFormatter called formatter and print the result of calling formatter.format.

Ruby

class MessageFormatter
  prepend GreetingPrepender

  def format
    "This is the original message."
  end
end

module GreetingPrepender
  def format
    "Hello! " + super
  end
end

# Create instance and print formatted message
# Your code here

Need a hint?

Create the instance with formatter = MessageFormatter.new and print with puts formatter.format.