What’s New in PHP 5

The long anticipated PHP 5 release comes with a slew of new features aimed at simplifying development with PHP. With PHP 5 comes the introduction of exception handling, the Standard PHP Library (SPL), enhanced support for XML, reflection, and quite a few enhancements to the object oriented features of the language. PHP 5 also offers a sizable list of new functions, many of which will not be covered in this article but are available in the manual.

XML

PHP 5 by default installs XML support and offers a new extension, SimpleXML. All XML functions are now standardized on the libxml2 library and are fully W3C standards compliant. SimpleXML is quite possibly the most valuable addition to PHP in years, providing a traversable structure to work on XML documents, allowing you to simply change values in the structure and write the file out with only a few lines of code. The XML functionality that has been available through PHP in the past has been quite rudimentary and required a fair amount of programming work to use, so it is not uncommon to see PHP 4 applications using XML without ever touching the xml functions.

PHP 5 also offers a replacement extension for DOMXL (available in “experimental” form in PHP 4) with the DOM extension. This extension allows you to work on your XML files using the DOM object model and is superior to SimpleXML particularly when you are not certain what document format to expect with your application. While DOM is more powerful, SimpleXML is much quicker to implement and easier to get a handle on for beginner programmers. Both of the extensions are robust and well thought out, and whichever suits your programming needs and taste, you will be using a powerful extension that is light years beyond what was available in PHP 4.

{mospagebreak title=Database Support}

PHP 5 offers some big enhancements to its ability to interact with databases. The most significant addition is the embedded SQLite database, a quick, lightweight database engine made specifically for embedded applications. This means there is no RDBMS process running on the server; SQLite reads and writes directly to files on disk. This results in significantly lower memory overhead when the database is not being used, but major performance problems arise if the system is used in a high traffic environment. SQLite is intended for small scale use, as best I can gather.

When testing it with small tables and less than one thousand rows per table, it was comparable to MySQL in executing simple joins with only one concurrent request, but performance from SQLite degraded exponentially with five or more concurrent connections coming in, which makes perfect sense. This is a good database solution for a small site that needs minimal features and expects minimal usage. It could also be useful for storing embedded configuration data in a PHP 5 application that may house its main data store in another RDBMS, and only run small queries against SQLite. SQLite is relatively standards compliant with a few major exceptions, most notably the lack of an ALTER TABLE statement.

PHP 5 also introduces support for the MySQL 4.1 client library with the introduction of the mysqli extension. The mysqli extension provides some basic objects for working with the MySQL server. The mysqli class is used as a connection object and as the ability to open and close connections as well as get context and state information from the server. The mysqli_stmt class represents a prepared statement that allows you to execute “prepare” and “execute” queries against the database. Lastly, the mysqli_result object provides a cursor based interface for reading results, providing similar functionality to the functions available in the standard MySQL extension using a MySQL resource handle. The new extension also adds support for SSL and input/output parameters. 

The last notable addition in the database area is enhanced support for Firebird/InterBase, an RDBMS that offers most ANSI SQL-92 features and runs on most operating systems. The ibase extension provides most of the same functionality for Firebird/InterBase as the new mysqli extension does for MySQL but in the same manner as the old MySQL extension – that is, no objects.

{mospagebreak title=SPL: Exceptions and Iterators}

PHP 5 comes with the Standard PHP Library (SPL), a collection of objects built to handle various tasks such as exception handling and object traversal (iteration). There are basically six groups of classes/interfaces available natively to the SPL.

  1. Iterators: SPL provides built in iterators to assist in a common task – object traversal. Iterators provide a way to traverse an object’s contents without exposing the inner workings of the object to the outside world. Iterators can be built to work on any data structure and provide a standardized interface. Some of the iterator classes and interfaces available in the SPL are: Iterator, OuterIterator, RecursiveIterator, IteratorIterator, ParentIterator, SeekableIterator, NoRewindIterator, and InifiniteIterator.

    Each iterator has a specific purpose and details can be found in the PHP manual.

  2. Directories: Two directory classes are available in the SPL: DirectoryIterator and RecursiveDirectoryIterator. These classes allow iterator based directory traversal and eliminates the need for messy directory handles.

  3. XML: There is one XML handling class in SPL, SimpleXMLIterator, which provides iteration over a simplexml object.

  4. Arrays: SPL offers something that has long been in need in PHP – ArrayObject and ArrayIterator. These object provide, as you may have guessed, an array object as well as an object to traverse the contents of an array without making assumptions on the way the array is storing it’s internal data.

  5. Counting: The SPL interface Countable allows you to hook into the standard array function count(), meaning you can use the count() function on a user defined object and get a meaningful result by implementing the Countable interface. This is very useful for non-simple data structures.

  6. Exceptions: Probably the biggest feature addition via the SPL, exceptions allow graceful error handling through try/catch blocks. The Exception class is simple to extend and the SPL provides a few standard classes of exceptions for common problems, such as LogicException, BadFunctionCallException, DomainException, OutOfRangeException, and InvalidArgumentException. Error handling has been a longtime problem in PHP and has resulted in some of the ugliest code I’ve ever seen, particularly using the PEAR error class. Exceptions should eliminate this sort of problem in the future.

{mospagebreak title=OOP: Object Enhancements}

PHP 5 makes leaps and bounds in its support for objects. Aside from all the new features, Zend claims to have addressed the performance problems involved with object creation and usage in previous versions of PHP, a fact that in itself should encourage more developers to use object-based PHP. PHP 5 offers enhancements in a few key areas including object autoloading, destructors, visibility, static methods, class constants, type hinting, interfaces, cloning, reflection and several magic methods.

Autoloading is a great new feature that provides a way for developers to make sure all dependencies for a class are in place before using it. If you attempt to instantiate a class that has not yet been defined, PHP 5 will call the __autoload() function as a last attempt to load the class before failing with an error. Since most developers put one class per file, and many classes often depend on another either by way of inheritance or encapsulation, __autoload() allows you to make sure all the necessary class files have been included. While PHP 4 had constructors, PHP 5 offers a new features: destructors. Destructors are called when an object is destroyed or all references to it have been removed. Destructors are implemented in classes by use of the __destruct function. The __construct function has also been introduced and takes precedence over the old-style constructor function. The old style still works, but it is recommended that __construct is used as it takes higher priority.

One of the biggest additions to PHP’s support for objects is visibility modifiers, also known as access modifiers. The var keyword has been deprecated and class variables are now to be declared as public, private, or protected. Public class variables are available to any other part of the program. Private variables are only available to that class. Protected variables are available to a class as well as its child classes, unlike private which only allows the class itself to access the variable. Methods can also be declared as public, private, or protected, and if none are declared a method is assumed to be public. Access modifiers allow PHP programmers to programmatically hide the inner workings of one object from another by preventing other objects from accessing class data directly. PHP 5 also introduces the static keyword. Static methods are called without an object instance and calls to static methods are resolved at compile time, not runtime. Static properties are accessed by the :: operator, not ->, and the special variable $this is not available in static methods.

Not only can you declares constants in C-style syntax, const constant = ‘constant value’;, but a class can contain it’s own constants and access them internally using self::constant. This simplifies management of constants and keeps them contained within the classes they belong to, preventing code clutter and conflicts with other constants in the same application that may need the same name but a different value. PHP 5 also allows type hints in method parameter declarations. If a parameter is given a type hint and an object of the wrong type is passed to it, PHP will generate a fatal error. It would be preferable for an exception to be thrown, but type hinting does at least allow responsibility to be placed in the calling code for making sure the proper data type is passed into a function call. Type hints can be used in any function, not strictly in class methods.

PHP 5 also introduces abstract classes and interfaces, which is probably THE most significant enhancement to the language. Abstract classes and interfaces allow high level design principles to be semantically applied to PHP classes. PHP includes three special method keywords, final, abstract and virtual, to facilitate the use of inheritance and interfaces. When a method is declared as final, it cannot be overridden by a child class. When a method is declared as abstract, it must be defined in a child class. When a method is declared as virtual, it may be inherited as is or overridden by a child class. When used in combination, abstract classes and interfaces enforce high level design throughout all levels of implementation and support properly coded objects. They can be used in excess, as can anything else, but used properly these are the most powerful tools available to object oriented developers.

The last features of note are object cloning, some more magic functions and the reflection class. Object cloning allows the implementation of a magic method, __clone() to define what exactly takes place when clone is called on an object. It allows developers to implement deep copying of object data when cloning without writing messy code. A few other noteworthy magic functions are __sleep() and __wakeup(), which are used in conjunction with serialize and unserialize to ensure proper destruction and recreation of resources used within an object. Additionally, the __toString magic method allows a class to decide how to react when it is used in string context. The reflection class works as the name implies; it allows developers to programmatically reverse-engineer classes, interfaces, functions and extensions. Reflection is a powerful tool in developing custom application frameworks.

Conclusion

Overall, PHP 5 offers dramatic improvements over PHP 4 in a lot of areas. These improvements are, by and large, geared toward advanced PHP developers. With the exception of the SimpleXML extension, most of the new functionality will probably have no appeal to the largest segment of the PHP programming population – that is, developers who look at PHP as a simple scripting language and use it to accomplish one task at a time. For PHP application developers though, I see PHP 5 quickly becoming the de facto standard. Start putting pressure on your hosts now to upgrade, because PHP 5 was definitely worth the wait.

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