And looking at all the edge-cases and possible data-races via tearing, declaring something as a value must be an explicit design decision that cannot be inferred by a compiler or optimizer alone.
But whether your data’s integrity can be broken by such must be decided by the class author.
Yes, exactly.
> So if you truly want the best performance (cache lines etc.) you must enable it.
Someone was saying that this is planned as an option in some future version of Java. As it stands, this is just not possible, and to me this suggests that the performance gains from Project Valhalla in this Java will be minimal.
Flattening has been the goal from the start, but it's simply not something that's delivered in this JEP. But even so, people should not overestimate the effect of values and flattening.
The biggest advantage will come from specialized libraries (stuff like OpenCV), and overall library enhancements (Tuples not requiring a dedicated indirection).