Hi,
> Apart from intellectual curiosity were you actually looking for this for a
> reason?
A bit of boh really, I’ve been profiling my App and the type of behaviour I
describe seems to be occurring. When I wrote:
myData = [self newData];
myNewData = [myData copy];
[myData release]; //If Non-ARC, removed
if ARC, I am using ARC.
I put a TO DO against it to try and check how much actual copying of data
(meaning more memory usage) was actually occurring, but it seems in most (if
not all) cases no actual data is being copied.
I was quite prepared to take the hit from the copy anyway, but it seems it
doesn't actually do any.
I realize this may change for any number of reasons, but right now, on the
config I am testing against, no data is being copied. I think it was in an
Apple Developer Videoand Keynote presentation from when the iPhone SDK was
first introduced or maybe V2 or V3 iOS SDK, but but I could be wrong.
Dave
On 27 Apr 2014, at 11:46, Roland King <r...@rols.org> wrote:
> 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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>>
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