> On Jul 12, 2017, at 4:15 PM, Quincey Morris > <quinceymor...@rivergatesoftware.com> wrote: > >> On Jul 12, 2017, at 14:57 , Jeremy Hughes <moon.rab...@virginmedia.com> >> wrote: >> >> I’m trying to understand memory management so I can avoid retain cycles and >> other issues. > > There’s nothing wrong with trying to understand. The bet you will (almost > always) lose is one involving reasoning about *when* retain counts reach > particular values (such as 1 or 0). > > I may be overlooking something important, but I see basically three tasks you > need to handle to avoid memory management bugs: > > 1. Strong references. > > In terms of object lifetimes, these are the easiest, because an object A that > depends on an object B’s existence and keeps a strong reference to B is doing > the right thing. There’s nothing here to worry about, assuming the reference > to B is released normally (and *automatically* usually) when A deallocates. > What you do have to worry about are reference cycles. You must either use > something like Instruments to find any, and either avoid creating them, or > ensure that you break them manually at a suitable time. > > 2. Weak references. > > This means zeroing weak references. (All weak references are zeroing since, > IIRC, macOS 10.6.8.) Again, there’s nothing to do here, except to ensure that > nothing crashes because a reference suddenly changes to nil. > > 3. Unowned/unsafe references. > > These are the killers. Typically, these are delegate references, but it’s > hard to keep track of all the possibilities. For example, NSWindow’s > “delegate” is still AFAIK unsafe. It’s usually set to the window controller, > but I’m not aware of any typical bugs arising from this reference becoming > invalid. The most common problem I know of is from table and outline view > delegate and data source references. In many cases, it’s wise to nil these > out manually when (say) your window closes.
We prefer to use "unretained" or "unsafe unretained" to describe this kind of reference. "Unowned" means something else in Swift. -- Greg Parker gpar...@apple.com <mailto:gpar...@apple.com> Runtime Wrangler _______________________________________________ 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
