The PHPro.org website has this new tutorial posted today - a step further into the would of OOP in PHP with a look at abstraction, hierarchies and polymorphism.

The PHP Object Oriented method of programming brings many exciting possibilities to application code. Many of the theories surrounding PHP Object Oriented code comes from some simple concepts. To the new comer, some of these concepts seem a little abstract, and with good reason. Abstraction is a key concept on Object Oriented code, but to the un-initiated, may seem rather vague.

Kevin looks at creating abstract classes as a foundation for types other classes can work from, overriding built in classes (like extending the DirectoryIterator to make a DirectoryReader class).