Rust's is built on top of (and exposed to) Iterators, which are a very general concept that can be rooted in all kinds of data structures, composed in all kinds of ways, and collected/processed in all kinds of ways (i.e. the user's code might not even contain an actual loop). The code continues to work in many situations, even where the optimization doesn't apply

You trade some special-case syntax and ergonomics for that generality, but it is very general even if not all of it is optimized in the same way