Programming iOS 6, 3rd Edition

Properties

A property is a syntactic feature of Objective-C 2.0 designed to provide an alternative to the standard syntax for calling an accessor method. As syntactic sugar for formally calling a method, you can append the property name to an instance reference using dot-notation. You can use the resulting expression either on the left side of an equal sign (to call the corresponding setter) or elsewhere (to call the corresponding getter). The name of the property relies, by default, on the accessor naming conventions.

I’ll use the Dog class as an example. If the Dog class has a public getter method called number and a public setter method called setNumber:, then the Dog class also has a number property. This means that, instead of saying things like this:

[fido setNumber: 42];
int n = [fido number];

You can talk like this:

fido.number = 42;
int n = fido.number;

Your use of property syntax is entirely optional. The existence of a property is equivalent to the existence of the corresponding getter and setter methods, and you’re free to call those methods by either syntax. When you use property syntax in code, it is translated behind the scenes into a call to the corresponding getter or setter method, so it’s all the same if you call the corresponding getter or setter method explicitly. In the case of Dog, you can use number as a property, or you can call the getter and setter methods number and setNumber:.

(Naturally, there are verbal quasi-religious wars on this topic, with one side claiming ...