L1330 - Truncated Character in Binary String

Warning

  karate() ->
    <<"空手🙂">>.
%%  ^^^^^^^^^ warning: character code larger than 255 will be truncated

Explanation

A binary text segment with no /utf8, /utf16, or /utf32 specifier is encoded using one byte per character (Latin-1), for historical reasons. Characters with code points above 255 do not fit in a single byte and are truncated, so the resulting binary represents different characters than the ones in the source code.

In the example, <<"空手🙂">> is silently encoded as <<"zKB">>.

%% Instead of:
karate() -> <<"空手🙂">>.

%% Write (UTF-8):
karate() -> <<"空手🙂"/utf8>>.

%% Or, since OTP 27, simply:
karate() -> ~"空手🙂".

This warning can be suppressed with -compile(nowarn_truncated_character), but note that the truncated result is almost never what you want. See also L1329.