On Aug 15, 2012, at 6:00 PM, Britt Durbrow wrote: > On Aug 15, 2012, at 4:46 PM, John McCall <rjmcc...@apple.com> wrote: >> On Aug 13, 2012, at 11:38 PM, Britt Durbrow wrote: >>> OK, I think I've isolated the issue... basically, __weak, @public, and >>> -fno-objc-arc don't like to play nice together. If you set a @public __weak >>> instance variable (may also apply to stack variables, I haven't tested that >>> yet) in a file compiled with -fno-objc-arc, and then access it in a file >>> compiled with ARC turned on, the variable gets zeroed out. >>> >>> I have reduced it to a simple test project, and I'm going to file a RADAR. >> >> Please do; maybe we can find a way to warn about the assignment to a __weak >> object in non-ARC. That said, your code is buggy; we do *not* guarantee >> anything about the representation of a weak object, and it is not legal to >> access one in non-ARC code except by explicitly calling one of the specified >> runtime functions (and we don't encourage you to do that). >> >> John. > > Done. rdar://12101247 > > The ARC documentation does not seem to indicate that the appropriate runtime > function is not emitted by the compiler when -fno-objc-arc is in effect... > and given that it's automatic *retain counting* that I thought I was turning > off; and not other parts of the runtime system, it's kinda counterintuitive > (well, it is to me at least :-) to have the compiler silently generate > erroneous code - especially when the result is a value changing on a *read* > operation!
Unless specifically indicated, everything in the ARC documentation is only enabled/valid under -fobjc-arc. ARC's __weak semantics are new to ARC. We did repurpose an existing "keyword" from GC, and it has roughly similar behavior, but that bites us here: __weak was always ignored when GC was disabled, so changing that is source-breaking. > I would expect either: a) the compiler would always emit the correct runtime > call for a __weak assignment no matter if ARC is on or off; or b) the > compiler would throw an error when an attempt to access a __weak variable is > made without ARC turned on (I don't think a warning is sufficient; given that > it really does mess things up). We'll see whether we can emit a warning. An error is unlikely. John. _______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
