Le 19 avr. 2010 à 20:54, Greg Parker a écrit : > On Apr 18, 2010, at 7:01 PM, Ken Thomases wrote: >> On Apr 18, 2010, at 7:14 PM, Dave DeLong wrote: >>> If I'm inside a method, is there a way to know at runtime whether that >>> method is a class or an instance method? >> >> Keep in mind that class methods are just instance methods, where the >> instance is the class object. (The class object being an instance of its >> metaclass.) >> >> So, in a deep sense, there's no distinction between a class method and an >> instance method. There's only the receiver object and the message/selector. > > Absolutely correct. But in practice, you can distinguish between class and > instance methods everywhere except the root class. > > The methods for a non-class instance are: > * your class's instance methods > * any superclass instance methods > * NSObject's instance methods > > The methods for a class instance are: > * the class's class methods > * any superclass class methods > * NSObject's class methods > * NSObject's instance methods > > That last line is the weird one. It's caused by the twist at the top of the > instance/class/metaclass diagram that makes all class objects into instances > of their root class (usually NSObject). > http://sealiesoftware.com/blog/archive/2009/04/14/objc_explain_Classes_and_metaclasses.html > > Comparing the two lists, you can see that the only overlap is NSObject's > instance methods. Everywhere else, you'll find that class methods are called > on class objects only, and instance methods are called on non-class objects > only. So "is self a class" will distinguish instance methods from class > methods, as long as you aren't writing instance methods on NSObject. > > Note that `[self class] == self` is the wrong check. Some classes lie about > [self class]. One specific case is KVO. On some OS versions, KVO creates > subclasses of observed classes at runtime. The subclasses override accessor > methods to add willChange/didChange notifications. The KVO-generated > subclasses override [self class] to return the non-KVO superclass instead of > the KVO-generated subclass.
If the test was [self class] == MyClass.class, it would be wrong, but this is not what he does, and AFAIK, [self class] returns self only for class objects. > You can use `object_getClass(self) == self` instead. object_getClass() never > lies. It will never be true as this test is equivalent to self->isa == self, and isa is never self. -- Jean-Daniel _______________________________________________ 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
