Why Included hook in Ruby? - Purpose & Use Cases

The Big Idea

What if your module could prepare any class automatically the moment it joins in?

The Scenario

Imagine you have many Ruby classes, and each needs to run some setup code whenever a module is included. Without a special way, you have to remember to call that setup manually in every class.

The Problem

This manual approach is slow and error-prone because you might forget to add the setup call in some classes. It also clutters your code with repetitive calls, making it hard to maintain.

The Solution

The Included hook lets you write code inside a module that automatically runs when the module is included in any class. This means setup happens by itself, keeping your code clean and reliable.

Before vs After

✗ Before

module M
  def self.setup(klass)
    klass.extend(ClassMethods)
  end
end

class C
  include M
  M.setup(self)
end

✓ After

module M
  def self.included(klass)
    klass.extend(ClassMethods)
  end
end

class C
  include M
end

What It Enables

It enables automatic, clean, and error-free setup whenever a module is included, making your Ruby code more elegant and maintainable.

Real Life Example

For example, when creating plugins or mixins that add methods or behavior to many classes, the Included hook ensures each class gets the right setup without extra code.

Key Takeaways

Manual setup for included modules is repetitive and risky.

Included hook runs code automatically on inclusion.

This keeps code cleaner and safer.