Desmond Hume Desmond Hume - 2 years ago 105
Objective-C Question

Is there a way to check if a string contains a Unicode letter?

In Cocoa, regular expressions are presumably following the ICU Unicode rules for character matching and the ICU standard includes character properties such as

for matching all kinds of Unicode letters. However

NSString* str = @"A";
NSPredicate* pred = [NSPredicate predicateWithFormat:@"SELF MATCHES '\\p{L}'"];
NSLog(@"%d", [pred evaluateWithObject:str]);

doesn't seem to compile:

Can't do regex matching, reason: Can't open pattern U_REGEX_BAD_INTERVAL (string A, pattern p{L}, case 0, canon 0)

If character properties are not supported (are they?), how else could I check if a string contains a Unicode letter in my iOS app?

Answer Source

The main point here is that MATCHES requires a full string match, and also, \ backslash passed to the regex engine should be a literal backslash.

The regex can thus be


Which means:

  • (?s) - enable DOTALL mode
  • .* - match 0 or more any characters
  • \p{L} - match a Unicode letter
  • .* - match zero or more characters.

In iOS, just double the backslashes:

NSPredicate * predicat = [NSPredicate predicateWithFormat:@"SELF MATCHES '(?s).*\\p{L}.*'"];

See IDEONE demo

If the backslashes inside the NSPrediciate are treated specifically, use:

NSPredicate * predicat = [NSPredicate predicateWithFormat:@"SELF MATCHES '(?s).*\\\\p{L}.*'"];
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