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
}

Bodywork

Answer 1

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];
}

Pulchia

Is the comparison necessary as [nil isEqual:uuid2] would also return NO, correct? – Bodywork

Answer 2

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];

Demerit

I would be interested in the reason for a down-vote. – Demerit

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 ;-). – Bodywork

Answer 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

Magnate

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. – Felisha

Answer 4

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]];
}

Bodywork