Share behavior with modules

Learn

A module can define methods for reuse. include makes its instance methods available to instances of the including class. Unlike a class, a module cannot create instances with new. A mixin is useful when several classes need behavior without sharing a superclass.

An included method runs on the receiving object. Named#label calls name on that same Product instance, so Product must supply a name method. Modules can also group constants under a namespace, but this example uses a module to share behavior.

Example

module Named
  def label
    "item: #{name}"
  end
end
class Product
  include Named
  def name
    "book"
  end
end
puts Product.new.label

Experiment

• Try Supply receiver behavior

  Predict the labels for these objects. Add another Product to products and check how the shared method uses each object's state.

• Try Reuse a mixin across classes

  Predict both labels. Add a third class that includes Named and defines its own name method. Call label on its instance.

Explore the official manual

• Official Ruby 3.2 documentation: Modules and Classes