Re: Implementing NSFastEnumeration

On Oct 2, 2009, at 0:21, Tom Hageman wrote:

> Hi Christiaan,
>
> On Thu, 1 Oct 2009 18:30:15 +0200, Christiaan Hofman wrote:
>>
>> [...] The
>> other thing is that I want to enumerate the underlying array of keys
>> first. I tried something along these lines:
>
> How about _replacing_ the key in itemsPtr[i] with the value as you go
> along?  Something like this: (Achtung, Mailware!)
>
> - (NSUInteger)countByEnumeratingWithState:(NSFastEnumerationState *) 
> state
> {
> 	NSUInteger i, count = [keys countByEnumeratingWithState:state
> objects:stackbuf count:len];
> 	for (i = 0; i < count; i++)
> 	{
> 		id key = state->itemsPtr[i];
> 		id value = [values objectForKey:key];
> 		state->itemsPtr[i] = value;
> 		//stackbuf[i] = value;
> 	}
> 	//state->itemsPtr = stackbuf;
> 	return count;
> }
>
>> While this works for small arrays, for larger arrays this gives a
>> memory access crasher. The reason seems to be that NSArray can return
>> more items than len (the size of stackbuf) in a single call.
>>
>> Would there be a way to modify this implementation to work? Or am I
>> forced to get the objects from keys without using fast enumeration  
>> (in
>> which case fast enumeration becomes hardly fast)?
>
> HTH,
> Regards,
>
> --Tom.


Well, I was wondering about whether that was safe. For instance, when  
the itemsPtr points directly to some internal C array of the keys  
array (rather than a copy), wouldn't this possibly modify this  
internal C array? In fact, when I tried this I got a crash.

Apart from that, Christopher Kane's comments still apply.

Christiaan