This is not an issue with the split implementation. Split is behaving correctly (according to the defined semantics of String). You'd get the exact same issue i

This is not an issue with the split implementation. Split is behaving correctly (according to the defined semantics of String). You'd get the exact same issue if you said str.index(of: ",") instead; in both cases, the "," is a Character, not a UnicodeScalar, and "," != ",\u{301}".