为什么= 32在32位与64位iOS设备上表现不同？

Question

I know in Objective-C == is very different from isEqual: . But I am curious about why the following code produces consistently different results on 32bit vs 64bit iOS devices.

NSIndexPath* a = [NSIndexPath indexPathForItem:0 inSection:0];
NSIndexPath* b = [NSIndexPath indexPathForItem:0 inSection:0];
NSLog(@"%@", a == b ? @"YES" : @"NO");
NSLog(@"%@", [a isEqual:b] ? @"YES" : @"NO");

On 32 bit device, eg iPhone 5, == always fails (expected).

2016-12-07 09:55:18.019 NSIndexPathTestObjc[18667:1958831] NO
2016-12-07 09:55:18.020 NSIndexPathTestObjc[18667:1958831] YES

On 64 bit device, eg iPhone 6s, == succeeds (unexpected).

2016-12-07 09:56:05.503 NSIndexPathTestObjc[18780:1960472] YES
2016-12-07 09:56:05.505 NSIndexPathTestObjc[18780:1960472] YES

Answer 1

I know in Objective-C == is very different from isEqual:

Yes -- you should use the latter to compare two objects. == only tells you whether the pointers you're comparing are the same.

But I am curious about why the following code produces consistently different results on 32bit vs 64bit iOS devices.

This is probably just be an implementation detail of -indexPathForItem:inSection: , where it might cache index paths that it generates on 64-bit systems and returns the cached object the second time you call the method with the same item, but doesn't on 32-bit systems. Don't rely on this behavior: use -isEqual: for object comparison.