> Type stability lets us mutably alias, which atomics and Cell do not. Well, that's not the case :) Both Cell and atomics let you mutably alias, in the sense

> Type stability lets us mutably alias, which atomics and Cell do not. Well, that's not the case :) Both Cell and atomics let you mutably alias, in the sense most languages mean. They don't let you mutably alias in the Rust `&mut` / "restrict" sense, which is far more powerful and would be unsound in any language, but they do let you mutably alias. > Vale also considers changing between Some<T> and None<T> to be a type-unstable operation, and the automatic borrow checker (HGM) detects the possibility for that (because the field was marked non-final), to not do auto-borrowing for it. We might decide to use something called the Undead Cycle to help with the Opt<T> case, though it comes with interesting tradeoffs. That's interesting and good to know! I'm glad you are taking this seriously. > There's a lot more to Vale, such as how our region borrow checker can enable zero-cost structured concurrency without the Send/Sync requirements, and the better RAII support. In the end, the only similarities we really share with Rust are the syntax and (hopefully!) the speed. A lot of the stuff in Rust is also found in other languages :) In this case, it sounds to me like Send/Sync are thoroughly built into your language, to the point that annotations are not needed--which is very nice, but not completely unique (this is the basis for memory safety in C# and Java, after all!), but may be so when combined with regions. From what it sounds like, though, I'm having a very hard time telling the difference between regions and (generational) arenas--they sound like they have almost exactly the same tradeoffs. Perhaps I'm missing something? Overall, seems like an interesting language, and I will definitely stay on the lookout.