Basic Autoloader Usage

Now that we have an understanding of what autoloading is and the goals and design of Zend Framework's autoloading solution, let's look at how to use Zend_Loader_Autoloader.

In the simplest case, you would simply require the class, and then instantiate it. Since Zend_Loader_Autoloader is a singleton (due to the fact that the SPL autoloader is a single resource), we use getInstance() to retrieve an instance.

require_once 'Zend/Loader/Autoloader.php';
Zend_Loader_Autoloader::getInstance();

By default, this will allow loading any classes with the class namespace prefixes of "Zend_" or "ZendX_", as long as they are on your include_path.

What happens if you have other namespace prefixes you wish to use? The best, and simplest, way is to call the registerNamespace() method on the instance. You can pass a single namespace prefix, or an array of them:

require_once 'Zend/Loader/Autoloader.php';
$loader = Zend_Loader_Autoloader::getInstance();
$loader->registerNamespace('Foo_');
$loader->registerNamespace(array('Foo_', 'Bar_'));

Alternately, you can tell Zend_Loader_Autoloader to act as a "fallback" autoloader. This means that it will try to resolve any class regardless of namespace prefix.

$loader->setFallbackAutoloader(true);

Warning

Do not use as a fallback autoloader

While it's tempting to use Zend_Loader_Autoloader as a fallback autoloader, we do not recommend the practice.

Internally, Zend_Loader_Autoloader uses Zend_Loader::loadClass() to load classes. That method uses include() to attempt to load the given class file. include() will return a boolean FALSE if not successful -- but also issues a PHP warning. This latter fact can lead to some issues:

If display_errors is enabled, the warning will be included in output.
Depending on the error_reporting level you have chosen, it could also clutter your logs.

You can suppress the error messages (the Zend_Loader_Autoloader documentation details this), but note that the suppression is only relevant when display_errors is enabled; the error log will always display the messages. For these reasons, we recommend always configuring the namespace prefixes the autoloader should be aware of

Note: Namespace Prefixes vs PHP Namespaces
At the time this is written, PHP 5.3 has been released. With that version, PHP now has official namespace support.
However, Zend Framework predates PHP 5.3, and thus namespaces. Within Zend Framework, when we refer to "namespaces", we are referring to a practice whereby classes are prefixed with a vender "namespace". As an example, all Zend Framework class names are prefixed with "Zend_" -- that is our vendor "namespace".
Zend Framework plans to offer native PHP namespace support to the autoloader in future revisions, and its own library will utilize namespaces starting with version 2.0.0.

If you have a custom autoloader you wish to use with Zend Framework -- perhaps an autoloader from a third-party library you are also using -- you can manage it with Zend_Loader_Autoloader's pushAutoloader() and unshiftAutoloader() methods. These methods will append or prepend, respectively, autoloaders to a chain that is called prior to executing Zend Framework's internal autoloading mechanism. This approach offers the following benefits:

Each method takes an optional second argument, a class namespace prefix. This can be used to indicate that the given autoloader should only be used when looking up classes with that given class prefix. If the class being resolved does not have that prefix, the autoloader will be skipped -- which can lead to performance improvements.
If you need to manipulate spl_autoload()'s registry, any autoloaders that are callbacks pointing to instance methods can pose issues, as spl_autoload_functions() does not return the exact same callbacks. Zend_Loader_Autoloader has no such limitation.

Autoloaders managed this way may be any valid PHP callback.

// Append function 'my_autoloader' to the stack,
// to manage classes with the prefix 'My_':
$loader->pushAutoloader('my_autoloader', 'My_');
 
// Prepend static method Foo_Loader::autoload() to the stack,
// to manage classes with the prefix 'Foo_':
$loader->unshiftAutoloader(array('Foo_Loader', 'autoload'), 'Foo_');