Include and Extend: Understanding Ruby on Rails Module Inclusion

A Deep Dive into the include and extend Methods

In Ruby on Rails, include and extend are used to add the functionality of a module to a class or an instance of a class. Both methods serve different purposes and are used in different scenarios. Here, we'll explain the differences between the two and provide examples to illustrate their usage.

Include

include: When a module is included in a class using include, the module's instance methods become available as instance methods of the class. This means that the module methods can be called on instances of the class, rather than the class itself.

Example:

In the example above, the Greetable module is included in the Person class. The greet method from the module is now available as an instance method on Person, so it can be called on an instance of Person.

Extend

extend: When a module is extended in a class using extend, the module's instance methods become available as class methods of the class. This means that the module methods can be called on the class itself, rather than instances of the class.

In the example above, the Greetable module is extended in the Person class. The greet method from the module is now available as a class method on Person, so it can be called on the Person class itself.

In summary, the main difference between include and extend is how the module methods are added to the class. include adds the module's methods as instance methods of the class, while extend adds the module's methods as class methods of the class.