In this latest tutorial on DevShed today, they look at methods to enforce the types of objects in a PHP4 environment.

When you are writing an object-based web application in PHP, you want to prevent your classes from being convoluted with input objects of the incorrect type. These input objects can cause the application to throw a fatal error. In this article, you will learn how to enforce object types in PHP 4.

By the end of this series, hopefully you'll have a clear idea of how to force object types inside of your PHP application, in this way avoiding further problems related to the so-called code contamination.

They start off with the creation of an (X)HTML widgets class to render certain page elements. Then, they show you the creation of a class to render the page and display them in a full document. There are examples of what happens when type checking isn't done and how to enforce the types inside of your class.