On Sep 21, 2016, at 21:10 , Doug Hill <cocoa...@breaqz.com> wrote: > > I believe the original question was why you can compare a string literal to > another object pointer using the == operator and it somehow works.
Actually, we’re more or less on the same page here, but for posterity… There’s no “somehow” with the == operator. It’s a C thing, not an Obj-C thing, so putting it between two pointers is well-defined, even if either of them happens to be an object reference. Indeed, constructs like "(void*)3" are also a C thing (any int can be cast to a pointer, provided the pointer size is at least as big as the int size on the architecture being compiled for). The original solution rested on a matter of *uniqueness* of pointers to string literals. The point was that the characters making up the string were never intended to be compared, only the pointers themselves, relying on the uniqueness of pointers to different string values. It’s an extremely delicate (that is, nerdy) distinction, but it’s clearer when you consider that a pointer comparison can always be assumed to be really, really cheap (1 machine instruction, almost always), whereas a string comparison can be quite expensive, quite apart from the question of whether objects or dynamism are involved. Another way of saying it is that the original solution leveraged the difference between literal string values without actually comparing them. That’s why it was clever (if only it wasn’t fatally flawed for a different reason). _______________________________________________ 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
