Hot on the heels of their previous patterns-related series, DevShed has posted this new tutorial with a look at the Visitor pattern, specifically as applied to objects.
You'll agree with me that one of the most interesting aspects of design patterns is precisely their practical side. Therefore, considering this undeniable fact, in conjunction with your permanent wish for extending your background in object-oriented programming with PHP, over the course of this series I'll be showing you some useful examples of how to build visitor objects, and more specifically how to include them in real-world applications.
They start with an example, complete with code, of a simple addElement call to store data in an array. The next logical step for storage is to an external resource, so they modify things slightly to write the data out to a file. Finally, they define the other side of things - the actual object that does the "visiting" to the previously defined classes.