On Tue, 01 Mar 2011 16:15:09 +0700, "Gerriet M. Denkmann" <gerr...@mdenkmann.de> said: > >On 1 Mar 2011, at 15:53, Kyle Sluder wrote: > >> On Tue, Mar 1, 2011 at 12:45 AM, Gerriet M. Denkmann >> <gerr...@mdenkmann.de> wrote: >>> So obviously NSAttributedString does NOT return [ [ aFont retain ] >>> autorelease ] but just some internal pointer. >>> >>> Is this documented somewhere? >> >> In the Memory Management Programming Guide: >> http://developer.apple.com/library/mac/#documentation/cocoa/conceptual/MemoryMgmt/Articles/mmAccessorMethods.html%23//apple_ref/doc/uid/TP40003539-SW6 >> >> --Kyle Sluder > >As far as I can see, this article talks about different ways to implement >setters and getters. >Do you want to imply that, whenever I get some object from AppKit, I have to >retain it until I no longer need it? > >Would be a safe thing to do. But also tedious. And in all my past experience >this was never necessary. >So I thought that the "Technique 1" of the linked article (returning >[[someObject retain] autorelease]) was the standart practice employed by >AppKit.
I've been thinking about this exchange, and I would propose that you consider it like this: Suppose you've got an NSArray and you fetch its element objectAtIndex:0. And suppose you now let go of the array (release) and it is destroyed. Do you expect the fetched element to persist without your having retained it? You do not; you know darned well that a collection doesn't behave like that. The collection *owns* its elements and will release them when it is released. All you got when you called objectAtIndex:0 was a pointer. If you want a share in its ownership, you must *take* ownership. Here's another example. Suppose you've got a UIView and you ask for its subviews. Do you imagine that asking for this property gives you ownership of those subviews? You do not. Similarly for *any* property of *any* object. You *never* imagine that a fetched property is somehow magically *giving* you ownership; it's just showing you a value. So what I'm trying to show you is that when you've got an object that owns stuff, you *never* expect that that object will dispense the stuff it owns while handing you a share in ownership. You *always* take ownership if you want that stuff to persist beyond the object that dispenses them. Ownership is *never* something you are magically given. It is always something that you must take if you want it. So, what I'm saying is, an NSAttributedString is like that. When it hands you that font, it's like an NSDictionary handing you some value for a particular key. What you *can* rely on is that a ***factory method*** will hand you an autoreleased object. So, [NSArray array] hands you an autoreleased array; it won't vanish right this second, but it will vanish when your code comes to an end, unless you retain it. You may be confusing this with that. Even in that case you don't have ownership; you just have some extra persistence time while your code continues to run. And this makes sense, because there is no other owning object. Hope that helps. m. -- matt neuburg, phd = m...@tidbits.com, <http://www.apeth.net/matt/> A fool + a tool + an autorelease pool = cool! Programming iOS 4! http://www.apeth.net/matt/default.html#iosbook_______________________________________________ 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: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
