Various experimental support has been added for value based classes in Valhalla. Quite a bit of these have acquired bit rot as the semantics of value/inline/primitive class types have evolved.

JEP390 formalizes the notion of value-based classes by introducing a JDK internal annotation @jdk.internal.ValueBased and requiring javac and JVM to implement various static and dynamic checks on such annotated types to mitigate/eliminate the migration pain when these classes eventually evolve to be primitive class types. This is work in progress on jep390 branch of Valhalla which would eventually make it to JDK16 and will be merged into Valhalla/lworld from jdk mainline.

All support that exists in Valhalla/lworld as of today should be withdrawn.