In this appendix, we saw that PHP5 has some new OOP extensions that are comparable with those of modern programming languages. They allow us to write very big applications while maintaining code reuse and cleanliness. Object-oriented programming is a natural solution for big projects such as content management systems or database libraries involving PDO. Libraries for PHP5 are now being written with object-oriented programming in mind.
However, this appendix just gives a short introduction to the main concepts behind OOP so that you can follow the code examples in this book. If you want to fully master object-oriented programming, you should refer to books that will introduce you to and guide you through this challenging topic.