Arguably an explicit type would have made the bug a little bit more obvious. You basically expect, by default, this kind of string manipulation functions to ret

Arguably an explicit type would have made the bug a little bit more obvious. You basically expect, by default, this kind of string manipulation functions to return a std::string. Obviously in this specific case you can return a view, and that makes it more performant; but it's kind of unexpected and using auto leaves the surprise a bit more hidden. But sure, you can still make the error with expiclit types.