Re: File Extensions Problem

FROM : Graham Cox
DATE : Fri Aug 29 02:12:30 2008

On 29 Aug 2008, at 4:28 am, Ken Thomases wrote:

> On Aug 27, 2008, at 5:59 PM, R.L. Grigg wrote:
>

>> Hmm, I guess the wrinkle in this particular case is if the 
>> "contract" doesnt specify something that the programmer assumes to 
>> be safe to do (like enumerating backwards), how can you know how to 
>> implement your end?

>
> Enumerating NSArrays backwards is safe and supported by the 
> framework.  The earlier discussion had to do with mutating a 
> collection while enumerating, which is explicitly stated to be 
> unsafe.  Somebody (I forget who) claimed that mutating was "safe" 
> while enumerating backwards, but they were wrong.  In this case, 
> their wrongness was not based on things left unsaid in the contract, 
> but on violating things explicitly laid out in the contract.



Well, that was me. But I do see the error of my ways... I guess it was 
Michael Ash's comment that NSArray *could* change its storage half way 
through enumeration (if the collection were mutated) that woke me up. 
I suspect it would only do this if the collection dramatically changed 
in size but clearly that wouldn't be something to rely on. I checked 
my own code to make sure I wasn't following my own "advice" anywhere 
and turns out I've never done it without making a copy anyway.

cheers, Graham