If your concurrency strictly can't involve parallelism then sure, no data races, but also then your performance is miserable on modern hardware.

If your concurrency can invoke parallelism, then you need to explicitly protect against data races, or else you need to define what happens (Java does this, nobody else has) or else you shrug and say too bad now the program is nonsense, you lose (C, C++, Go, many modern languages do this, it is easier)

> If your concurrency strictly can't involve parallelism then sure, no data races, but also then your performance is miserable on modern hardware.

Often worth it when that hardware is battery-powered though. Using those extra cores isn't free.

Ownership hasn’t shipped yet.

It has an ABI-level ownership thing already. What's missing is ways to control it.