On Mon, Oct 3, 2011 at 11:23 AM, Charles Srstka <cocoa...@charlessoft.com> wrote: > 1. Apple reserves the underscore prefix for their own use, so you could, at > least theoretically, clash with a superclass ivar this way, and
[snip] > > 3. If I use an ivar prefix that no one else uses (as far as I know), then I > can make my class into a subclass of something from a publicly available > framework without needing to worry about ivar name clashes. This only matters at compile time. If you have a class that subclasses a framework class, and you add an ivar named "_foo", later releases of the OS can add an ivar named "_foo" and your application will continue to run on the latest release without issue. (Well, on 32-bit Mac OS X, they can rename an existing ivar to "_foo" without issue; adding an ivar will trigger the Fragile Base Class problem.) On 32-bit Mac OS X, ivar accesses get translated into an offset. "self->_foo = 42" gets translated into something like "*(self + 18) = 42". On 64-bit Mac OS X and on iOS, ivar access is done indirectly via symbol. "self->_foo = 42" gets translated into something like "*(self + OBJC_IVAR_$_MyClass__foo) = 18". Neither of these methods actually cares what the ivar is named (the compiler could generate offset symbols based on the days of the week if it wanted to). > > 2. KVO’s “access instance variables directly” (mis)feature recognizes the > underscore prefix. I like to give it a prefix that KVO doesn’t know about so > that I can be sure never to end up accidentally accessing the ivars of > another object without going through the proper accessors. This is indeed a good reason to avoid using plain underscores. I hate this misfeature so much. --Kyle Sluder _______________________________________________ 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
