Rust is not zero cost abstractions, they make decision on case-by-case basis.

It's their tagline and it's how it feels. I cen freely abstract. Zig is kind of making me index into byte array all the time.

Rust may feel like this in general, but I seen multiple discussions when people spot cases where rust is much slower than C++, they start looking at them, and the finding is that Rust is not zero-cost abstraction, and induce penalty sometime, while C++ is always zero cost abstraction.