Open Radar

 
Summary:
Empty NSTaggedPointerString returns YES to isEqualToString:nil

An empty NSTaggedPointerString returns YES to isEqualToString:nil. This differs from other NSString implementations, such as __NSCFConstantString.

=code=

#import <Foundation/Foundation.h>
#import <objc/runtime.h>

int main(int argc, char *argv[]) {
    @autoreleasepool {
        NSString *a = @"";
        NSLog(@"a: '%@' %@", a, object_getClass(a));
        NSLog(@"[a isEqualToString:nil] => %i", [a isEqualToString:nil]);
        
        NSString *b = [[@"string" mutableCopy] copy];
        NSLog(@"b: '%@' %@", b, object_getClass(b));
        
        NSString *c = [b substringWithRange:NSMakeRange(0,0)];
        NSLog(@"c: '%@' %@", c, object_getClass(c));
        NSLog(@"[c isEqualToString:nil] => %i", [c isEqualToString:nil]);
    }
}

=output=

2016-01-26 03:30:43.470 Untitled[82359:4491298] a: '' __NSCFConstantString
2016-01-26 03:30:43.471 Untitled[82359:4491298] [a isEqualToString:nil] => 0
2016-01-26 03:30:43.471 Untitled[82359:4491298] b: 'string' NSTaggedPointerString
2016-01-26 03:30:43.471 Untitled[82359:4491298] c: '' NSTaggedPointerString
2016-01-26 03:30:43.471 Untitled[82359:4491298] [c isEqualToString:nil] => 1

=end=

Steps to Reproduce:
1. Run the above using Xcode 7.1

Expected Results:
I'd expect all members of the NSString class-cluster to behave the same. No string can be equal to nil, so that method should always return NO. -isEqual: returns NO.

Actual Results:
The NSTaggedPointerString returns YES, but other implementations return NO.

Version:
OS X 10.11 (15A284)

Notes:
Currently the workaround is just to use -isEqual:.

Configuration:
Xcode 7.1
Mac OS X 10.11

Attachments: