Stephen, thanks to your detailed answer. This absolutely explains the observed behavior, but still leaves me wondering about the feature of sending messages to id. While I am still new to programming in objective-c and only having read the basic language documentation, I remember this feature to be pointed out as a helpful tool. But after this discovery, I can only mark it as a "don't use" language feature.
Regards, Philipp Am 10.04.2011 um 10:00 schrieb Stephen J. Butler: > On Sat, Apr 9, 2011 at 9:52 AM, Philipp Leusmann <m...@byteshift.eu> wrote: >> Who can explain this behavior to me? Why is oWidth != object.mWidth ? How >> can that happen? > > It's an artifact of how Objective-C searches for selector > implementations. You're calling @selector(width) on an "id", and of > course "id" doesn't implement @selector(width). > > So what Objective-C does is search for the first implementation of > @selector(width) that it finds. My guess is it finds the one in AppKit > first (greping the frameworks): > > NSTableColumn.h:- (CGFloat)width; > > Then when the compiler sets up the call site it does it expecting a > CGFloat return and that is handled differently than an integer. So the > call site and the implementation of how your width is done disagree > and you get some strange heisenvalue back. > > When you cast the variable to "Result*", Objective-C now knows to use > YOUR implementation of @selector(width) and it sets up the call site > properly. _______________________________________________ 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
