The final lifecycle callback is the Class#inherited method, which is invoked whenever a given Class is sub-classed. It receives exactly one parameter, which is the sub-class (again, not the name of the sub-class, but rather the sub-class itself).

Here's an exercise so you can get your feet wet.

class Room @@subclasses = [] def self.subclasses @@subclasses end end

[reset] Need a hint? See the Solution

Hint

Implement inherited as a self method on Room and store the parameter it receives in @@subclasses.

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With this, we're done with Ruby's Object Lifecycle Callbacks. Use them sparingly, use them well.

Here's a final exercise to keep them fresh in your mind. It's based on a common pattern seen in many Ruby gems. All you should do is add the lifecycle callbacks containing code necessary to make the tests pass.

module Gym module ClassMethods def build end end module InstanceMethods def open end def book_for_practice end def close end end end

[reset] Need a hint? See the Solution

Hint

Add an included callback to Gym that in turn includes Gym::InstanceMethods into the target class and extends the target with Gym::ClassMethods.

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