Modeling Illegal States

How to use sealed hierarchies to shift away from exceptions thereby preventing runtime errors, enforcing assumptions, recovering the ability to reason locally and achieving linear code flow.

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THE CURRENT VERSION OF THIS ARTICLE IS PUBLISHED HERE.

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Tags: #FUNDAMENTAL CONCEPT

This article is part of the Kotlin Primer, an opinionated guide to the Kotlin language, which is indented to help facilitate Kotlin adoption inside Java-centric organizations. It was originally written as an organizational learning resource for Etnetera a.s. and I would like to express my sincere gratitude for their support.

It is recommended to read the Introduction before moving on. Check out the Table of Contents for all articles.

Take a look at the following code, which is basically a template for every business rule ever written: