Did you think rust doesn’t free up memory for you? That would be the biggest memory leak in history! No! Rust does reference counting, it just makes sure that that number is always one! What did you think the borrow checker was for?

There is no runtime garbage collection in Rust. Given a legal program, it can detect where free-type instructions are needed at compile time, and adds them. From there on it works like C, but with no memory leaks or errors because machines are good at being exactly correct. If you want to say that’s just a reference counting algorithm that’s so simple it’s not there, sure, I guess you can do that.

Roc has runtime overhead to do garbage collection, it says so right on their own page. It might be a post-Rust language but this feels like the same conversation I’ve had about D and… I can’t even remember now. Maybe Roc is a cool, innovative language. It’s new to me. But, it doesn’t sound like it’s doing anything fundamentally new on that specific part.

Edit: Reading your follow up to the other person, it sounds like it has both a Rust-style compile time algorithm of some sort, and then (reference count-based) garbage collection at run time for parts of the program that would just be illegal in Rust.