Programming iOS 6, 3rd Edition

An Instance Reference Is a Pointer

In C, every variable must be declared to be of some type. In an object-based language such as Objective-C, an instance’s type is its class. The C language includes very few basic data types. To facilitate the multiplicity of class types required by its object-based nature, Objective-C takes advantage of C pointers. So, in Objective-C, if a variable is an instance of the class MyClass, that variable is of type MyClass* — a pointer to a MyClass. In general, in Objective-C, a reference to an instance is a pointer and the name of the data type of what’s at the far end of that pointer is the name of the instance’s class.

Tip

Note the convention for capitalization. Variable names tend to start with a lowercase letter; class names tend to start with an uppercase letter.

As I mentioned in Chapter 1, the fact that a reference to an instance is a pointer in Objective-C will generally not cause you any difficulties, because pointers are used consistently throughout the language. For example, a message to an instance is directed at the pointer, so there is no need to dereference the pointer. Indeed, having established that a variable representing an instance is a pointer, you’re likely to forget that this variable even is a pointer and just work directly with that variable:

NSString* s = @"Hello, world!";
NSString* s2 = [s uppercaseString];

Having established that s is an NSString*, you would never dereference s (that is, you would never speak of *s) to access ...