> On Aug 10, 2017, at 9:44 AM, Alastair Houghton <alast...@alastairs-place.net> 
> wrote:
> On 10 Aug 2017, at 15:24, Jeremy Hughes <moon.rab...@virginmedia.com 
> <mailto:moon.rab...@virginmedia.com>> wrote:
>>> On 10 Aug 2017, at 15:15, Alastair Houghton <alast...@alastairs-place.net 
>>> <mailto:alast...@alastairs-place.net>> wrote:
>>> On 10 Aug 2017, at 15:09, Charles Srstka <cocoa...@charlessoft.com 
>>> <mailto:cocoa...@charlessoft.com>> wrote:
>>>> They’re equivalent syntactically, but performance-wise, +array and friends 
>>>> will cause the object to be put into an autorelease pool. Therefore, +new 
>>>> is better for performance.
>>> Not with ARC they don’t.  The ARC logic circumvents the autorelease pool in 
>>> that case.
>> Are you sure?
> Yes, I’m sure.  At the call site, ARC causes the compiler to emit a call to 
> objc_retainAutoreleasedReturnValue() or 
> objc_unsafeClaimAutoreleasedReturnValue(), while in the method itself, ARC 
> will use objc_autoreleaseReturnValue() or 
> objc_retainAutoreleaseReturnValue().  The latter looks at the code for the 
> call site and, assuming it matches, it will *not* do the autorelease and will 
> set a flag that causes objc_retainAutoreleasedReturnValue() to eliminate the 
> retain.

The frameworks (and thus, the implementation of +array) are not built using 
ARC. The -autorelease method is called manually, and the object is put in the 
autorelease pool. You can see this for yourself by making a small test app that 
calls [NSMutableArray array] and running it in Instruments, where the 
autorelease will be clearly visible.



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