Valhalla inline classes - created in Java, used in Kotlin

lenivchick.lazyteam · May 16, 2021, 6:07pm

Hello everyone! I understand that I can’t create inline class with more than one field in Kotlin (yet). But can I use inline classes created in Java? I’ve tried and got this:

java.lang.IllegalStateException: Could not read class: VirtualFile: <My inline java class>.class

Tried -XXLanguage:+InlineClasses, -jdk-home points to JDK with Valhalla support, -jvm-target 14.

If what I’m trying to do is possible - what else I need to do to make kotlinc understand compiled Java inline classes?

Wasabi375 · May 17, 2021, 9:08am

Kotlin doesn’t support valhalla inline classes. Right now kotlin inline classes and valhalla inline classes are 2 completly different things. In the future kotlin will combine both concepts into so called value classes. However this is still in the desing phase and I doubt there will be much work on supporting valhalla before we get a release date for it.
If you want more information you should read through this KEEP:

github.com

Kotlin/KEEP/blob/master/notes/value-classes.md

# Design Notes on Kotlin Value Classes

* **Type**: Design notes
* **Author**: Roman Elizarov
* **Contributors**: Alexander Udalov, Andrey Breslav, Dmitry Petrov, Ilmir Usmanov, Ilya Gorbunov, Marat Akhin, Maxim Shafirov, Mikhail Zarechenskiy, Stanislav Erokhin  
* **Status**: Under consideration
* **Discussion and feedback**: [KEEP-237](https://github.com/Kotlin/KEEP/issues/237)

This is not a design document, but an exploratory description of the current state of value classes in Kotlin and potential ways for their future evolution. The purpose of this document is to define a common terminology, provide some insight into potential avenues for features that are based on value classes, and thus establish a channel for discussion with the Kotlin community on use-cases for these features, their potential syntax, impact on existing Kotlin code, etc.

We, in the Kotlin team, are aware of and try to follow 
[minus 100 points](https://docs.microsoft.com/en-us/archive/blogs/ericgu/minus-100-points)
language design rule.  Any new feature in the language has to clear a high bar on utility it brings to compensate for the complexity it will entail. This document lists a lot of ideas that are complex both conceptually and in terms of implementing them in the compiler. The decision on whether they are that much useful to be added into the language is still to be made.

**Table of contents**

<!--- TOC -->

* [Introduction](#introduction)
  * [Built-in primitive value classes](#built-in-primitive-value-classes)

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lenivchick.lazyteam · May 17, 2021, 9:24am

Oh

I guess I have no choice but writing a precompiler that substitutes “fallback” non-valhalla classes when needed.

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Valhalla inline classes - created in Java, used in Kotlin

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