Programming Ruby 3.3 (5th Edition, p 122): Unicode Character Definition Incorrect


On page 122, in the discussion of “Strings and Encodings”, it is stated: “A Unicode character is two bytes long, which makes a Unicode string twice as long internally as a Latin-1 string.” This is incorrect. Unicode represents a 21-bit code space; two bytes are not enough to cover it.

The Unicode Standard says, "Unicode characters are represented in one of three encoding forms: a 32-bit form (UTF-32), a 16-bit form (UTF-16), and an 8-bit form (UTF-8). The 8-bit, byte-oriented form, UTF-8, has been designed for ease of use with existing ASCII-based systems. "

I’d further argue that this is not just being pedantic: the idea that Unicode can be captured completely in two bytes is one of the more dangerous lingering misconceptions. It leads people to think that UTF-16, for instance, will always be 2-byte units (it is, like UTF-8, a variable-length encoding).