What's new in PHP 5?

Most noteworthy in the new release is the Zend Engine 2.0, what one might call the core of PHP. The Zend Engine is responsible for parsing and executing PHP code, implements PHP's data structures, memory and resource management and more. With the 5.0 release, there are quite a few changes in the Zend Engine. No major version release would be complete without performance tweaks, and PHP 5 is no exception. This release includes a new memory manager, designed with muli-threaded environments in mind.

Naturally, PHP 5 includes some language changes. One interesting addition is the introduction of private and protected member variables. This allows PHP developers to decide whether or not they wish to make a variable visible to a class that extends a class the variable is extended in (protected) or set variables to be visible only to the class that they are declared in (private).

PHP 5 also introduces destructors for objects, something that was missing in PHP 4. (Constructors were present in PHP 4, but behaved differently.) This allows developers to define a destructor for an object that can perform a task when the last reference to an object is destroyed.

XML support has been beefed up in PHP 5. The XML extensions in PHP 5 are based on the Libxml2 library from the GNOME project. PHP 5 supports SAX, which was present in PHP 4, and adds support for the W3C DOM standard, XSLT and SOAP. The changes are covered in some detail in this article. There is also the SimpleXML extension.

Developers who use PHP in conjunction with MySQL will be interested in the MySQLi extension. This extension gives developers access to functions in MySQL 4.1.2 and above. This version supports prepared statements, SSL, transaction control and a number of other features present in MySQL 4.1 and above.

If MySQL isn't to your tastes, the SQLite extension is bundled with PHP 5. SQLite is a C library that implements a SQL database engine which does not require a separate SQL server. For lightweight installations or situations (such as shared hosting) where a PHP developer does not have access to MySQL or another SQL server, this may be of great interest. SQLite requires no configuration, implements much of SQL92 and supports databases up to 2 terabytes.

There are also quite a few new functions in PHP 5 that are worth looking into for PHP developers. The ChangeLog lists the new functions added in PHP 5, most of which (if not all) are already documented in the PHP Manual.

For more cautious PHP developers and users, PHP 4.3.8 was also released last Tuesday to address several security problems that have come to light since the release of PHP 4.3.7. If not upgrading to 5.0, users should be sure to upgrade to the 4.3.8 release.

In all, the PHP 5 release looks like a nice step forward for the PHP project. The changes to PHP 5 should inflict minimal, if any, pain on developers who have been developing on PHP 4.