On Dec 27, 2012, at 21:58 , Rick Aurbach <r...@aurbach.com> wrote: > Rick, > > I'm no Obj-C language expert; in fact I'm pretty much a newbie. But I have > had some experience with smart pointers (boost, etc) from my C++ case. > > Here's how I think of strong and weak references in ARC. (If the following is > wrong, I'm sure someone more knowledgeable than myself will set us both > straight.) > > Weak references never increment the retain count. > > They are simply pointers which are automatically nil-ed when the object's > retain count reaches 0 (and is hence deallocated). So, in your method, you > create an object with [NSMutableData data] and assign it to a weak pointer. > It's retain count is 1. At the end of the method, this object has its retain > count decremented. Since its count is now 0, it is deallocated and the weak > reference to it is set to 0. > > In your case, this is confusing because you've combined two statements into > one. The logic of your line of code is really > id temp = [NSMutableData data]; > mInputBuffer = temp; > > In this formulation, it is clear that the temp is deallocated when the method > exits. Combining these two statement in a way that hides the temporary does > not automagically promote the weak pointer to being a strong one. > > Hope this helps.
Not really. I may not have been clear. This is in an Objective-C object, just compiled in a .mm file so I can call some other C++ code. But the object in question, and the ivar mInputBuffer, are all Obj-C. So, the usual bit about references being weak by default in C structs (and C++ classes) doesn't hold here. > > > On Dec 27, 2012, at 2:00 PM, cocoa-dev-requ...@lists.apple.com wrote: > >> I just wrote some Objective-C++ code. It's basically just a regular Obj-C >> class, but makes some C++-style calls in its methods. >> >> Anyway, I added an NSMutableData* ivar to my class, and set it with >> >> mInputBuffer = [NSMutableData data]; >> >> in one of the methods. Subsequent accesses, however, have resulted in it >> being deallocated, even though I never set mInputBuffer to NULL anywhere. >> >> I changed the code to refer to it via a strong property, and it's fine. >> >> I thought ARC worked the same in both cases (that is, retained the object on >> assignment and kept it around until the last reference was gone, even if via >> a regular ivar) >> >> A bit of googling confirms this, so I'm wondering what I've done wrong. >> >> -- >> Rick > > Cheers, > > Rick Aurbach, Ph.D. > > > > > > > _______________________________________________ > > 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/rmann%40latencyzero.com > > This email sent to rm...@latencyzero.com -- Rick _______________________________________________ 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
