Open Radar

 
Summary:
In iOS7, the hash implementation for UIMutableIndexPath and NSIndexPath appear to have changed. If you have a mutable and non-mutable index path with the same value, they return true for isEqual: but have differing hash values. In iOS6 the hash values would be equal.

The UITableViewDelegate method - (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath provides a UIMutableIndexPath. If, for example, the program keeps an NSSet of NSIndexPaths and checks the membership of the supplied indexPath, there will be false negatives due to the hash difference.

Steps to Reproduce:
Run the attached Xcode project, or:

Implement the UITableViewDelegate method
 - (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath

with the following code (or similar):
- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath
{
    CGFloat retVal = 50.0f;

    NSIndexPath *copiedIndexPath = [NSIndexPath indexPathForRow:indexPath.row inSection:indexPath.section];

    NSLog(@"=============== heightForRowAtIndexPath: =============== ");
    NSLog(@"copiedIndexPath: '%@' indexPath: '%@'", copiedIndexPath, indexPath);
    NSLog(@"[copiedIndexPath class]: '%@' [indexPath class]: '%@'", [copiedIndexPath class], [indexPath class]);
    NSLog(@"isEqual: %@", [indexPath isEqual:copiedIndexPath] ? @"YES" : @"NO");
    NSLog(@"[copiedIndexPath hash]: '%u' [indexPath hash]: '%u'", [copiedIndexPath hash], [indexPath hash]);

    if ([indexPath isEqual:copiedIndexPath] && indexPath.hash != copiedIndexPath.hash)
    {
        NSLog(@"ERROR: If isEqual: evaluates to YES then both object's hash values should also be equal.");
    }
    
    return retVal;
}


Expected Results:
The if statement would never evaluate to true and no "ERROR" log statement would be output.

Actual Results:
For all indexPath's greater than [0,0] the if evaluates to true and an error was output:

2014-08-21 16:06:09.369 IndexPathBug[69261:60b] =============== heightForRowAtIndexPath: =============== 
2014-08-21 16:06:09.370 IndexPathBug[69261:60b] copiedIndexPath: '<NSIndexPath: 0x8c7c160> {length = 2, path = 0 - 0}' indexPath: '<UIMutableIndexPath 0x8c7c050> 2 indexes [0, 0]'
2014-08-21 16:06:09.370 IndexPathBug[69261:60b] [copiedIndexPath class]: 'NSIndexPath' [indexPath class]: 'UIMutableIndexPath'
2014-08-21 16:06:09.370 IndexPathBug[69261:60b] isEqual: YES
2014-08-21 16:06:09.371 IndexPathBug[69261:60b] [copiedIndexPath hash]: '22' [indexPath hash]: '22'
2014-08-21 16:06:09.371 IndexPathBug[69261:60b] =============== heightForRowAtIndexPath: =============== 
2014-08-21 16:06:09.371 IndexPathBug[69261:60b] copiedIndexPath: '<NSIndexPath: 0xa5b08a0> {length = 2, path = 0 - 1}' indexPath: '<UIMutableIndexPath 0xa56abc0> 2 indexes [0, 1]'
2014-08-21 16:06:09.371 IndexPathBug[69261:60b] [copiedIndexPath class]: 'NSIndexPath' [indexPath class]: 'UIMutableIndexPath'
2014-08-21 16:06:09.372 IndexPathBug[69261:60b] isEqual: YES
2014-08-21 16:06:09.372 IndexPathBug[69261:60b] [copiedIndexPath hash]: '16406' [indexPath hash]: '22'
2014-08-21 16:06:09.372 IndexPathBug[69261:60b] ERROR: If isEqual: evaluates to YES then both object's hash values should also be equal.
2014-08-21 16:06:09.373 IndexPathBug[69261:60b] =============== heightForRowAtIndexPath: =============== 
2014-08-21 16:06:09.373 IndexPathBug[69261:60b] copiedIndexPath: '<NSIndexPath: 0xa577d60> {length = 2, path = 0 - 2}' indexPath: '<UIMutableIndexPath 0xa56d2d0> 2 indexes [0, 2]'
2014-08-21 16:06:09.373 IndexPathBug[69261:60b] [copiedIndexPath class]: 'NSIndexPath' [indexPath class]: 'UIMutableIndexPath'
2014-08-21 16:06:09.373 IndexPathBug[69261:60b] isEqual: YES
2014-08-21 16:06:09.373 IndexPathBug[69261:60b] [copiedIndexPath hash]: '32790' [indexPath hash]: '16406'
2014-08-21 16:06:09.374 IndexPathBug[69261:60b] ERROR: If isEqual: evaluates to YES then both object's hash values should also be equal.

etc.

Interestingly, the hashes for the mutable and non-mutable seem to be "off by one" (if you compare the various row values you will note that the previous row value will have the same hash...)

For instance:

[0, 4]
UIMutableIndexPath hash: '98326'
NSIndexPath hash: '131094'
[0, 5]
UIMutableIndexPath hash: '131094'
NSIndexPath hash: '163862'

Note, the [0, 4] NSIndexPath hash is the same as the [0, 5] UIMutableIndexPath hash (both are 131094).

Version:
iOS SDK 7.1

Notes:


Configuration:
All iOS 7 simulators.

Attachments:
'IndexPathBug.zip' was successfully uploaded.

Dupe of 15806671