Xcode 7.3 beta 5 errors on __weak in manual reference counting
Closed this issue · 6 comments
Specific error is in CDRSpyInfo.mm and says:
"cannot create __weak reference in file using manual reference counting", this error can be turned off in the build settings, but then an error regarding "No matching function for call to objc_loadWeak" crops up (same error but also for objc_storeWeak)
Reference https://openradar.appspot.com/24791037
Thanks for opening this issue @codeman9 -- I hadn't been aware of this breakage in the betas.
I don't have an answer to this issue right now -- it looks like we'll need to either investigate moving this over to ARC (which may be very hard to get right), or find another way of creating a weak reference. It's a little frustrating that Apple seems to be implying that weak references never worked outside of ARC, because I'm fairly certain I've actually seen __weak resolve retain cycles when ARC wasn't being used. Maybe I'm wrong.
My understanding of these statements is that the __weak attribute never actually did anything in MRC, which isn't surprising to me at all. In MRC all references are effectively weak anyway, it just means that the auto-zeroing behavior wasn't available unless you called down to objc_storeWeak and objc_loadWeak yourself, which is what Cedar is doing here.
I've pushed 9ab7ca0 which seems to resolve the issue by just removing the annotation. The variable names still contain the word weak so the intention is still reasonably documented. @codeman9 could you check and see if this works on your end?
Under MRC references are assign, not weak -- an important difference if
relying on the value of the pointer (null/not null). An assign reference
can be non-null, but point to garbage, whereas weak is guaranteed to be nil
or point to something valid.
I have a feeling there is reliance on this value distinction in the code
these days, so we should be careful here.
On Sun, Mar 6, 2016 at 05:26 Brian Croom notifications@github.com wrote:
My understanding of these statements is that the __weak attribute never
actually did anything in MRC, which isn't surprising to me at all. In MRC
all references are effectively weak anyway, it just means that the
auto-zeroing behavior wasn't available unless you called down to
objc_storeWeak and objc_loadWeak yourself, which is what Cedar is doing
here.I've pushed 9ab7ca0
9ab7ca0
which seems to resolve the issue by just removing the annotation. The
variable names still contain the word weak so the intention is still
reasonably documented. @codeman9 https://github.com/codeman9 could you
check and see if this works on your end?—
Reply to this email directly or view it on GitHub
#376 (comment).
Good call @akitchen. I think the salient point here though is that __weak under MRC has never actually provided zeroing weak references, they were still just standard assign references after all. That's why the code using these variables calls into objc_storeWeak and objc_loadWeak to manually invoke the runtime magic that provides the nil-after-dealloc behavior.
Yup, I completely agree. I think the key word here is "magic"
On Sun, Mar 6, 2016 at 07:46 Brian Croom notifications@github.com wrote:
Good call @akitchen https://github.com/akitchen. I think the salient
point here though is that __weak under MRC has never actually provided
zeroing weak references, they were still just standard assign references
after all. That's why the code using these variables calls into
objc_storeWeak and objc_loadWeak to manually invoke the runtime magic
that provides the nil-after-dealloc behavior.—
Reply to this email directly or view it on GitHub
#376 (comment).
@briancroom The changes you pushed removed the errors for me. Thanks!