NSString instance reports its class as NSCFString

Question

My objective here is really simple -- I'm trying to set an NSString to some test data, then return the class, which should be NSString. Here's my code:

NSString* stringer = [NSString stringWithFormat: @"Test"];
NSLog(@"%@", [stringer class]);

The log says that the class is NSCFString, not NSString. What's going on here?

Standee

Answer 1

NSString is really a container class for different types of string objects. Generally an NSString constructor does return an object that is actually of type NSCFString, which is a thin wrapper around the Core Foundation CFString struct.

Varden

Answer 2

NSString is a class cluster, along with other Foundation types such as NSNumber and NSArray:

Class clusters are a design pattern that the Foundation framework makes extensive use of. Class clusters group a number of private, concrete subclasses under a public, abstract superclass. The grouping of classes in this way simplifies the publicly visible architecture of an object-oriented framework without reducing its functional richness. Class clusters are based on the Abstract Factory design pattern discussed in “Cocoa Design Patterns.”

Etrem

Why did Apple not follow this approach for NSOrderedSet? A NSOrderedSet behaves exactly like a NSArray at the interface level, yet they made a independent class for it. – Eleaseeleatic