objective-c – NSPointerArray奇怪的压缩

我有一个很弱的NSPointerArray与一些已经被释放的NSObject.在打电话之前,我看到的是：

(lldb) po [currentArray count]
1
(lldb) po [currentArray pointerATindex:0]
<nil>
(lldb) po [currentArray allObjects]
<__NSArraym 0x16f04f00>(

)

这是有道理的,但真正奇怪的是,当我在该数组上调用compact时,我看到相同的值！ Count仍然返回1,而pointerATindex：0为零.

为什么没有被删除？

编辑

这是完整的代码(是的,它是XCTesTing框架)：

- (void)TESTCompaction {
    __weak id tesTingPointer = nil;

    NSPointerArray *weakArray = [NSPointerArray weakObjectsPointerArray];

    @autoreleasepool {

        NSObject *someObj = [[NSObject alloc] init];

        tesTingPointer = someObj;

        [weakArray addPointer:(__bridge void*)tesTingPointer];

        NSLog(@"before compaction inside autorelease: tesTingPointer = %@ count = %d,allObjects = %@,pointerATindex:0 = %@,pointerATindex:0 class = %@",tesTingPointer,[weakArray count],[weakArray allObjects],[weakArray pointerATindex:0],[(id)[weakArray pointerATindex:0] class]);

        someObj = nil;
    }

    NSLog(@"before compaction outside autorelease: tesTingPointer = %@ count = %d,[(id)[weakArray pointerATindex:0] class]);

    [weakArray compact];

    NSLog(@"after compaction outside autorelease: tesTingPointer = %@ count = %d,[(id)[weakArray pointerATindex:0] class]);
}

和日志：

before compaction inside autorelease: tesTingPointer = <NSObject: 0x7de7ff80> count = 1,allObjects = (
    "<NSObject: 0x7de7ff80>"
),pointerATindex:0 = <NSObject: 0x7de7ff80>,pointerATindex:0 class = NSObject
2015-07-20 14:27:14.062 AppetizeSuite copy[54144:9019054] before compaction outside autorelease: tesTingPointer = (null) count = 1,allObjects = (
),pointerATindex:0 = (null),pointerATindex:0 class = (null)
2015-07-20 14:27:22.615 AppetizeSuite copy[54144:9019054] after compaction outside autorelease: tesTingPointer = (null) count = 1,pointerATindex:0 class = (null)

为什么compact方法不删除第一个指针？在打电话前显然是零.