Hate to be a pedant, but that's really not what "zero cost abstractions" means. The idea behind those is that you get a cleaner interface to some gross machine functionality/OS API/etc. layer, but don't pay a performance cost vs. using the gross lower-level layer. E.g. Rust's Option, unlike C++'s std::optional.

What you're thinking of is "no runtime" or "lightweight runtime", which does often mean "no garbage collector".

Rust's zero cost abstractions mainly stem from its affine ownership model managing memory lifetimes safely and correctly with zero cost - as that is the killer feature... That's what I do.

When people think of "zero cost" they don't think about std::optional. They think about not having to manage memory lifetimes AND NOT having to pay for a Garbage Collector to do it for you. That was always the trade you made until Rust.

I add on some cost to locks to prevent deadlock, and some cost to loops to insert co-operative yields in concurrent contexts unless you turn it off.