PHP 5 has significantly improved support for object-oriented programming (OOP). This is a major change and a key reason to upgrade your code from PHP 4. If you’re a fan of OOP, you will be very happy with the tools PHP 5 provides you.
Early versions of PHP were strictly procedural: you could define functions, but not objects. PHP 3 introduced an extremely rudimentary form of objects, written as a late-night hack. Back in 1997, nobody expected the explosion in the number of PHP programmers, or that people would write large-scale programs in PHP. Therefore, these limitations weren’t considered a problem.
Over the years, PHP gained additional object-oriented features; however, the development team never redesigned the core OO code to gracefully handle objects and classes. As a result, although PHP 4 improved overall performance, writing complex OO programs with it is still difficult, if not nearly impossible.
PHP 5 fixes these problems by using Zend Engine 2 (ZE2). ZE2 enables PHP to include more advanced object-oriented features, while still providing a high degree of backward compatibility to the millions of PHP scripts already written.
If you don’t have experience with object-oriented programming outside of PHP, then you’re in for a bit of a surprise. While some of the new features allow you to do things more easily, many features don’t let you do anything new at all. In many ways, they restrict what you can do.
Even though it seems counterintuitive, ...