Herman: Shipping Rust in Firefox

I don't know about C#, but: more specifically, Java was (like, 20 years ago) advertised as having concurrency built-in but it doesn't really have any real safeguards against improper use of concurrency. It's all synchronization primitives or classes like ConcurrentSkipListMap which don't really make it hard to create race-free programs. You have to think hard, and I mean *hard* about concurrency and synchronization and races. Java 8's parallel Streams are much, much better in this regard, though (streams are similar to what in Rust is called iterators, and parallel streams are what the rayon crate implements).

I can only imagine that in C++ it's even worse :)