Use NS_RETURNS_RETAINED macro to save time #843
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maicki
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Mar 18, 2018
bernieperez
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Apr 25, 2018
* Use NS_RETURNS_RETAINED macro to save time * Update changelog and do the thing with the license headers
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ARC has a tricky time returning stuff, since it doesn't know whether the caller was written with ARC or not. Under ARC, you don't really need the autorelease pool, but under MRR it's really useful. So when ARC goes to return something from a non-
init/copy/create/newmethod, it uses two functionsobjc_retainAutoreleaseReturnValueandobjc_retainAutoreleasedReturnValue. The first one, on the callee side, unwinds the stack and checks if the second one is present on the caller side. If so, it skips the autorelease pool to save resources. Great trick!But we don't need to spend that effort. We can annotate methods to say "yeah despite the name, I'm going to return you a +1 straight up." Then ARC will skip those two functions and just do the right thing. So, if we have users who are writing in MRR then this is breaking API since we'll be giving them +1s, not autoreleased objects. But obviously nobody is writing client code in MRR now.
It would be very nice to make, say
-layoutSpecThatFitsuse this attribute, but that would require all implementors to add theNS_RETURNS_RETAINEDmacro to their implementations, since the macro HAS to be present on both the declaration and implementation sides. Maybe worth doing if we have a big release, but otherwise not worth irritating our users for.