ok but you can't rely on any of this behaviour, because the only defined
interface is copy (or copyWithZone) and mutableCopy (or rather
mutableCopyWithZone). If NSMutableData is smart enough to do copy-on-write then
that's great.
I've certainly never seen any apple documentation which discusses the details
of how objects do and don't copy, perhaps you were reading someone else's
analysis.
Apart from intellectual curiosity were you actually looking for this for a
reason?
On 27 Apr, 2014, at 6:32 pm, Dave <d...@looktowindward.com> wrote:
> Hi,
>
> Yes, I can see there are no guarantees and if is *has* to copy the object it
> will, but it has some optimisations, take this for example:
>
> -(NSData*) newData
> {
> NSData* myData;
>
> myData = [[NSData alloc] init];
> //Add data to myData
>
> return myData;
> }
>
> -(void) someMethod
> {
> NSData* myData;
> NSData* myNewData;
>
> myData = [self newData];
> myNewData = [myData copy];
>
> [myData release];
>
> //Do something the myNewData
>
> }
>
> I think it said, in cases like this, no real data would be copied. It also
> said something like, the same would be true if it were using NSMutableData,
> as long as “myData” is NOT mutated before it is released.
>
> It’s these types of cases I’m talking about, I realize that if objects start
> mutating then physical copies need to be made in some cases. it’s just it
> doesn't happen automatically just because you have invoked copy or
> mutableCopy - physical copies only occur IF they need to.
>
> Thanks
> Dave
>
> On 27 Apr 2014, at 10:00, Dave <d...@looktowindward.com> wrote:
>
>> Hi All,
>>
>> A long time back, I remember reading something about the way in which copy
>> and mutableCopy are implemented. I think basically it said that:
>>
>> someObject = [someOtherObject copy];
>>
>> or
>>
>> someObject = [someOtherObject mutableCopy];
>>
>> Wouldn’t necessarily allocate any extra data storage. I’ve been searching
>> for it to refresh my memory, but I can’t see to find it anywhere. Does
>> anyone know if this document or something like it exists somewhere?
>>
>> Thanks a lot
>> Dave
>>
>>
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