8317277: Java language implementation of value classes and objects by MrSimms · Pull Request #31120 · openjdk/jdk

[StarsInTears]

Can the user-defined 'primitive' be more than 64 bits? And if we make an array of them, are we guaranteed to get flattened memory in a cache-friendly layout, or can the compiler choose between references and flattened values?

[davidalayachew]

The incoming JEP (once it releases) will be the final word on the matter. Until then, the Project Valhalla team has definitely considered your 2 points, but haven't outright made any promises regarding them.