Calorion
commented
1 month ago Yes, Apple uses ICU pretty much everywhere. It's very similar to PCRE, except it lacks \K, but it's apparently based on Java. From https://unicode-org.github.io/icu/userguide/strings/regexp.html:
Differences with Java Regular Expressions
- ICU does not support UREGEX_CANON_EQ. See https://unicode-org.atlassian.net/browse/ICU-9111.
- The behavior of \cx (Control-X) differs from Java when x is outside the range A-Z. See https://unicode-org.atlassian.net/browse/ICU-6068.
- Java allows quantifiers (*, +, etc) on zero length tests. ICU does not. Occurrences of these in patterns are most likely unintended user errors, but it is an incompatibility with Java. https://unicode-org.atlassian.net/browse/ICU-6080
- ICU recognizes all Unicode properties known to ICU, which is all of them. Java is restricted to just a few.
- ICU case insensitive matching works with all Unicode characters, and, within string literals, does full Unicode matching (where matching strings may be different lengths.) Java does ASCII only by default, with Unicode aware case folding available as an option.
- ICU has an extended syntax for set [bracket] expressions, including additional operators. Added for improved compatibility with the original ICU implementation, which was based on ICU UnicodeSet pattern syntax.
- The property expression \p{punct} differs in what it matches. Java matches matches any of !"#$%&'()*+,-./:;<=>?@[]^_
{|}~. From that list, ICU omits $+<=>^|~ - ICU follows the recommendations from Unicode UTS-18, http://www.unicode.org/reports/tr18/#Compatibility_Properties. See also https://unicode-org.atlassian.net/browse/ICU-20095.
Hmm, so I'm trying to figure out what engine does Swift uses and it seems based on this sources, 1 . https://developer.apple.com/documentation/foundation/nsregularexpression
It is essentially PCRE?