The Evolution of the PHP Object Type

This first incarnation of object-oriented programming (OOP) support covered only the barest implementation of object-related characteristics. In the words of one core developer, "A PHP4 object is just an Array with some functions bolted onto the side." It is this generation of PHP objects that you'll explore now.

With the second major release of the Zend Engine (ZE2) found in PHP5, several new features found their way into PHP's OOP implementation. For example, properties and methods may now be marked with access modifiers to make them inaccessible from outside your class definition, an additional suite of overloading functions are available to define custom behavior for internal language constructs, and interfaces can be used to enforce API standards between multiple class chains. When you reach Chapter 11, "PHP5 Objects," you'll build on the knowledge you gain here by implementing these features in PHP5-specific class definitions.

Implementing Classes