How to compare NSUUID

Question

What is the best (least code, fastest, most reliable) way to compare two NSUUIDs?

Here is an example:

-(BOOL)isUUID:(NSUUID*)uuid1 equalToUUID:(NSUUID*)uuid2
{
    return ... // YES if same or NO if not same
}

Fruity Geek · Accepted Answer · 2013-12-11T19:00:33.577

12

From the NSUUID class reference:

Note: The NSUUID class is not toll-free bridged with CoreFoundation’s CFUUIDRef. Use UUID strings to convert between CFUUID and NSUUID, if needed. Two NSUUID objects are not guaranteed to be comparable by pointer value (as CFUUIDRef is); use isEqual: to compare two NSUUID instances.

So just use the following:

-(BOOL)isUUID:(NSUUID*)uuid1 equalToUUID:(NSUUID*)uuid2
{
    return [uuid1 isEqual:uuid2];
}

edited Dec 11 '13 at 19:00

answered Dec 11 '13 at 17:31

Fruity Geek

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2

Is the comparison necessary as [nil isEqual:uuid2] would also return NO, correct? – Joshcodes Dec 11 '13 at 18:36

score 8 · Answer 2 · answered Dec 11 '13 at 17:45

8

You don't need to create an extra method for this, as the documentation states that

NSUUID objects are not guaranteed to be comparable by pointer value (as CFUUIDRef is); use isEqual: to compare two NSUUID instances.

So just do BOOL sameUUID = [uuid1 isEqual:uuid2];

answered Dec 11 '13 at 17:45

tilo

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I would be interested in the reason for a down-vote. – tilo Dec 11 '13 at 17:49
The "extra method"'s purpose is only to explain the question further. I'd be interested in the reason for a down-vote on the question too ;-). – Joshcodes Dec 11 '13 at 18:38

score 3 · Answer 3 · answered Dec 29 '17 at 00:03

3

NSUUID effectively wraps uuid_t.

Solution...

@implementation  NSUUID ( Compare )



- ( NSComparisonResult )  compare : ( NSUUID * )  that
{
   uuid_t   x;
   uuid_t   y;

   [ self  getUUIDBytes : x ];
   [ that  getUUIDBytes : y ];

   const int   r  = memcmp ( x, y, sizeof ( x ) );

   if ( r < 0 )
      return  NSOrderedAscending;
   if ( r > 0 )
      return  NSOrderedDescending;

   return  NSOrderedSame;
}



@end

answered Dec 29 '17 at 00:03

digitaldaemon

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This is so important, since NSSortDescriptor uses compare: method. I used NSFetchedRequest with NSPredicate and NSSortDescriptor that was sorting by uuid attribute and got crash (no compare: selector is present with NSUUID) - this fixed it. Thank you. – Nick Apr 25 '19 at 11:54

score 0 · Answer 4 · answered Dec 11 '13 at 17:23

A reasonable simple way to accomplish this is to use string comparison. However, a method that utilizes the underlying CFUUIDRef may be faster.

-(BOOL)isUUID:(NSUUID*)uuid1 equalToUUID:(NSUUID*)uuid2
{
    return [[uuid1 UUIDString] isEqualToString:[uuid2 UUIDString]];
}

How to compare NSUUID

4 Answers4