Question

When performing introspection on a class, I use the following code:

if([object isKindOfClass:[NSNumber class]]){

        NSLog(@"I am an NSNumber: %@", object);
    }

 NSLog(@"Properties:%@", [object class]);

The output is:

I am an NSNumber: 320
Properties:__NSCFNumber

Can anyone explain why the result is __NSCFNumber for type NSNumber? I also noticed NSArray is identified as:

__NSArrayI

Answer 1

NSNumber is a class cluster. NSNumber is the abstract, public superclass of several concrete subclasses. When you create an NSNumber with any of the +numberWith... methods, you will get an instance of one of these subclasses.

When you pass an object to NSLog() as a parameter corresponding to a “%@” storage specifier, NSLog() will send that object a -description message, and insert whatever’s returned from that message expression into the string it writes to the stderr file descriptor.