ASCII bytes

as_types returns a slice of bytes &[u8] representing the string's UTF-8 encoded data. Rust string must be valid UTF-8, but not ASCII.

ASCII vs UTF-8

American Standard Code for Information Interchange, a 7-bit encoding standard.

UTF-8, a variable-length Unicode Encoding, backward-compatible with ASCII. SUpport over 1million Unicode charactors, including (latin, Chineses, etc.). use 1-4 bytes, 1 for ASCII, 2-4 for others. Unicode is over 1.4 million code points, not for encoding.