Objective-C Programming: The Big Nerd Ranch Guide

22 Class Extensions

So far, you have declared all of your properties, instance variables, and methods in the class header file. The header is where a class advertises its properties and methods so that other objects will know how to interact with it.

However, not every property or method should be advertised in a class’s header. Some properties or methods may only be intended for use by the class or instances of the class. Such internal details are better declared in a class extension. A class extension is a set of declarations that is private. Only the class or instances of the class are able to use the properties, instance variables, or methods declared in a class extension.

For example, the officeAlarmCode property of BNREmployee ...