Why is self allowed in static context in objective c

Question

Why is using self allowed in static context in Objective-C?

I thought it was allowed and then I encountered memory errors that took me a week to find out that self is not an alias for calling other static methods from the class instead of typing the class name.

Xcode and its compiler seems very smart at finding common pitfalls, why isn't it even generating a warning about something like that?

Answer 1

1. There is no such thing as a "static context" in Objective-C. What we have instead are "class methods". They definitely are not "static" methods.
2. Class methods (ones prefixed with a +) are really just instance methods on a particular Class object. (did your mind just explode?) And since you have a self variable accessible in an instance method, you naturally have a self variable accessible in the class method as well.
3. In a class method, self points to the class itself.
4. Just as you can do [self performAction] inside an instance method to invoke methods on this particular instance, you can do [self performClassAction] inside a class method to invoke methods on this particular class.
5. All Class objects are subclasses of NSObject. So you can use any NSObject instance method on any Class object. (did your mind just explode again?)

Answer 2

self is only allowed within the context of an Objective-C method. By "static context" I assume you mean within a class method (that is, one whose signature starts with + rather than -.) Your assertion that "self is not an alias for calling other static methods" is incorrect.

self is allowed in those cases so that you can:

1. pass the class around as an object, since all Objective-C classes are themselves objects
2. send messages to a class without specifying the class name, in case a method is overridden in a subclass ([Foo bar] will use Foo's implementation always; [self bar] will use whatever implementation is available in self.)