Incidentally, that function could be s.iter().rev().position(|ss| ss == key), or drop the `rev()` and use `.rposition(...)` if one wants indices from the start

Incidentally, that function could be s.iter().rev().position(|ss| ss == key), or drop the `rev()` and use `.rposition(...)` if one wants indices from the start of the slice. Although I'm not sure how searching a slice of strings for a specific one is related to UTF-8: the &str's are used completely opaquely. Did you mean to be searching a &str itself?