指向接口'NSDate'的指针的算法，它在非脆弱的ABI中不是常量

Question

在下一个obj-c代码中出现问题。

if (fabs(originalLocation.timestamp - ((CLLocation *)[lastLocations objectAtIndex:i]).timestamp) > constAverageLocationTimeout) 
{ 
    //do 
}

xCode发送错误：

error: Semantic Issue: Arithmetic on pointer to interface 'NSDate', which is not a constant size in non-fragile ABI

有任何想法吗？

Answer 1

你的程序（以及编译器错误的位置）如果你把它分解一下会更有意义。也许是这样的：

NSDate * orginalDate = originalLocation.timestamp;
CLLocation * lastLocation = [lastLocations objectAtIndex:i];
NSDate * lastDate = lastLocation.timestamp;

NSTimeInterval originalTime = [originalDate timeIntervalSinceReferenceDate];
NSTimeInterval lastTime = [lastDate timeIntervalSinceReferenceDate];
NSTimeInterval elapsed = fabs(originalTime - lastTime);

if (elapsed > constAverageLocationTimeout) {
  /* do */
}

具体而言，timestamp是NSDate类型的属性，而不是标量数字，例如NSTimeInterval。