On Dec 28, 2009, at 3:27 PM, Graham Cox wrote:
>
> On 29/12/2009, at 4:00 AM, Joar Wingfors wrote:
>
>>> NSInteger i = 0;
>>> while ([[self trackingAreas] count]==0) {
>>> [self removeTrackingArea:[[self trackingAreas]
>>> objectAtIndex:i]];
>>> i++;
>>> }
>>
>>
>> That loop seems all kinds of wrong... ;-)
>>
>> How about:
>>
>> for (NSTrackingArea *trackingArea in [self trackingAreas]) {
>> [self removeTrackingArea:trackingArea];
>> }
>
>
> Wouldn't this fall foul of the usual problem with deleting items from the
> collection being iterated, in that it will skip every other object? (Or
> perhaps fast enumeration has a built-in protection against that?)
Yes, fast enumeration specifically states:
Enumeration is “safe”—the enumerator has a mutation guard so that if you
attempt to modify the collection during enumeration, an exception is raised.
And also:
Since mutation of the object during iteration is forbidden, you can
perform multiple enumerations concurrently.
>
> The first loop is also wrong in that its terminating condition is backwards
> (should be >0) as well as having the skip every other object problem. If you
> want to remove items from the collection being iterated, you should copy the
> collection temporarily and iterate that or iterate it by index backwards.
>
Cheers,
. . . . . . . . Henry
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