Inline (Value) Classes

An introduction to inline (also called value) classes, how they’re connected to Project Valhalla, their properties & limitations, and how to use them to prevent runtime errors, push code up the call stack, and thereby write safer code.

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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.

Kotlin supports inline classes, which are a subset of value classes. An inline class allows the compiler to optimize away wrapper types, i.e. types that only contain a single other type. They are basically primitive classes…