Tracking state with the Observer pattern

The Observer pattern is a concept in which an object allows us to subscribe to the changes of its state and notifies a set of its observers automatically whenever there is a change of the object state. The implementation of the Observer pattern in Kotlin is pretty easy with the help of the built-in Observable property delegate offered by the standard library. In this recipe, we are going to implement an observable variable that will allow us to subscribe to the changes in its state. The subscribed listener should be notified immediately after any state updates. In the following example, we are going to declare the temperature: Int variable and subscribe to its changes.

How to do it...

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