Object-Oriented PHP

Objects Need Access Modifiers

OOP is made possible by using this simple concept of a class as a cohesive aggregate of characteristics and behaviors—as you'll see in Chapter 3, this is exactly what objects are in PHP 4—but one of the most important features of any OO language is the use of access modifiers. Access modifiers refine the object model by controlling how an object is used or reused. Simply put, access modifiers provide guidance about what you can and cannot do with an object. To get a sense of what this means, let's use an example from procedural programming.

Let's define a subroutine as a function that is never invoked directly but that is only called by other functions. Now suppose you're a procedural programmer with a library ...