Advanced PHP Programming By George Schlossnagle

Over the past three years PHP has evolved from being a niche language used to add dynamic functionality to small sites to a powerful tool making strong inroads into large-scale, business-critical Web systems.

The rapid maturation of PHP has created a skeptical population of users from more traditional "enterprise" languages who question the readiness and ability of PHP to scale, as well as a large population of PHP developers without formal computer science backgrounds who have learned through the hands-on experimentation while developing small and midsize applications in PHP.

George Schlossnagle is a principal at OmniTI Computer Consulting, a Maryland-based tech company that specializes in high-volume Web and email systems. Before joining OmniTI, he led technical operations at several high-profile community Web sites, where he developed experience managing PHP in very large enterprise environments. He is a frequent contributor to the PHP community and his work can be found in the PHP core, as well as in the PEAR and PECL extension repositories.

Before entering the information technology field, George trained to be a mathe-matician and served a two-year stint as a teacher in the Peace Corps. His experience has taught him to value an interdisciplinary approach to problem solving that favors root-cause analysis of problems over simply addressing symptoms.

While there are many books on learning PHP and developing small applications with it, there is a serious lack of information on "scaling" PHP for large-scale, business-critical systems. Schlossnagle's Advanced PHP Programming fills that void, demonstrating that PHP is ready for enterprise Web applications by showing the reader how to develop PHP-based applications for maximum performance, stability, and extensibility.

THIS BOOK STRIVES TO MAKE YOU AN expert PHP programmer. Being an expert programmer does not mean being fully versed in the syntax and features of a language (although that helps); instead, it means that you can effectively use the language to solve problems. When you have finished reading this book, you should have a solid understanding of PHP's strengths and weaknesses, as well as the best ways to use it to tackle problems both inside and outside the Web domain.

This book aims to be idea focused, describing general problems and using specific examples to illustrateas opposed to a cookbook method, where both the problems and solutions are usually highly specific. As the proverb says: "Give a man a fish, he eats for a day. Teach him how to fish and he eats for a lifetime." The goal is to give you the tools to solve any problem and the understanding to identify the right tool for the job.

In my opinion, it is easiest to learn by example, and this book is chock full of practical examples that implement all the ideas it discusses. Examples are not very useful without context, so all the code in this book is real code that accomplishes real tasks. You will not find examples in this book with class names such as Foo and Bar; where possible, examples have been taken from live open-source projects so that you can see ideas in real implementations.

When I started programming PHP professionally in 1999, PHP was just starting its emergence as more than a niche scripting language for hobbyists. That was the time of PHP 4, and the first Zend Engine had made PHP faster and more stable. PHP deployment was also increasing exponentially, but it was still a hard sell to use PHP for large commercial Web sites. This difficulty originated mainly from two sources:

Perl/ColdFusion/other-scripting-language developers who refused to update their understanding of PHP's capabilities from when it was still a nascent language.

Java developers who wanted large and complete frameworks, robust object-oriented support, static typing, and other "enterprise" features.

Neither of those arguments holds water any longer. PHP is no longer a glue-language used by small-time enthusiasts; it has become a powerful scripting language whose design makes it ideal for tackling problems in the Web domain.

A programming language needs to meet the following six criteria to be usable in business-critical applications:

Fast prototyping and implementation

Support for modern programming paradigms

Scalability

Performance

Interoperability

Extensibility

The first criterionfast prototypinghas been a strength of PHP since its inception. A critical difference between Web development and shrink-wrapped software development is that in the Web there is almost no cost to shipping a product. In shipped software products, however, even a minor error means that you have burned thousands of CDs with buggy code. Fixing that error involves communicating with all the users that a bug fix exists and then getting them to download and apply the fix. In the Web, when you fix an error, as soon as a user reloads the page, his or her experience is fixed. This allows Web applications to be developed using a highly agile, release-often engineering methodology.

Scripting languages in general are great for agile products because they allow you to quickly develop and test new ideas without having to go through the whole compile, link, test, debug cycle. PHP is particularly good for this because it has such a low learning curve that it is easy to bring new developers on with minimal previous experience.

PHP 5 has fully embraced the rest of these ideas as well. As you will see in this book, PHP's new object model provides robust and standard object-oriented support. PHP is fast and scalable, both through programming strategies you can apply in PHP and because it is simple to reimplement critical portions of business logic in low-level languages. PHP provides a vast number of extensions for interoperating with other servicesfrom database servers to SOAP. Finally, PHP possesses the most critical hallmark of a language: It is easily extensible. If the language does not provide a feature or facility you need, you can add that support.