Prepend for method chain insertion in Ruby

Introduction

Prepend lets you add a module's methods before others in a class. This helps change or add behavior without changing original code.

You want to add extra steps before existing methods run.

You need to fix or change behavior in a class without editing it directly.

You want to share common behavior across classes by inserting modules.

You want to keep original methods but add new features before them.

Syntax

Ruby

module YourModule
  def method_name
    # new behavior
    super  # calls original method
  end
end

class YourClass
  prepend YourModule
end

Use prepend inside the class to insert the module before the class in method lookup.

Calling super inside the module method runs the original method.

Examples

This example adds a greeting before the original hello method.

Ruby

module Greeting
  def hello
    puts "Hi!"  # new behavior
    super       # call original
  end
end

class Person
  def hello
    puts "Hello from Person"
  end
  prepend Greeting
end

Person.new.hello

Logger module prepends to add logging before saving.

Ruby

module Logger
  def save
    puts "Logging before save"
    super
  end
end

class Record
  def save
    puts "Saving record"
  end
  prepend Logger
end

Record.new.save

Sample Program

This program shows how prepend inserts Announcer before Speaker. The speak method in Announcer runs first, then calls the original speak.

Ruby

module Announcer
  def speak
    puts "Starting to speak..."
    super
  end
end

class Speaker
  def speak
    puts "Hello, world!"
  end
  prepend Announcer
end

Speaker.new.speak

Important Notes

Prepend changes the order Ruby looks for methods, putting the module first.

Use super in the module method to run the original method after your added code.

Prepend is useful for adding behavior without rewriting or copying code.

Summary

Prepend inserts a module before a class in method lookup.

It lets you add or change behavior by running module methods first.

Use super in the module to call the original method.