I assumed `c` was a `String` - my code should be `c.into_bytes()`. If you have a str, then of course mutating the bytes directly is unsafe. Also, `str::make_as

I assumed `c` was a `String` - my code should be `c.into_bytes()`. If you have a str, then of course mutating the bytes directly is unsafe. Also, `str::make_ascii_uppercase` would require using `get_mut` which does utf-8 checks.