The first time an instance of the autoloader is retrieved, it registers itself with spl_autoload. You retrieve an instance using the getInstance() method:

$autoloader = Zend_Loader_Autoloader::getInstance();

By default, the autoloader is configured to match the "Zend_" and "ZendX_" namespaces. If you have your own library code that uses your own namespace, you may register it with the autoloader using the registerNamespace() method. For instance, if your library code is prefixed with "My_", you could do so as follows:

$autoloader->registerNamespace('My_');

You can also register arbitrary autoloader callbacks, optionally with a specific namespace (or group of namespaces). Zend_Loader_Autoloader will attempt to match these first before using its internal autoloading mechanism.

As an example, you may want to utilize one or more eZcomponents components with your Zend Framework application. To use its autoloading capabilities, push it onto the autoloader stack using pushAutoloader():

$autoloader->pushAutoloader(array('ezcBase', 'autoload'), 'ezc');

This tells the autoloader to use the eZcomponents autoloader for classes beginning with "ezc".

You can use the unshiftAutoloader() method to add the autoloader to the beginning of the autoloader chain.

By default, Zend_Loader_Autoloader does no error suppression when using its internal autoloader, which utilizes Zend_Loader::loadClass(). Most of the time, this is exactly what you want. However, there may be cases where you want to suppress them. You can do this using suppressNotFoundWarnings():

$autoloader->suppressNotFoundWarnings(true);

Finally, there may be times when you want the autoloader to load any namespace. For instance, PEAR libraries do not share a common namespace, making specifying individual namespaces difficult when many PEAR components are in use. You can use the setFallbackAutoloader() method to have the autoloader act as a catch-all:

$autoloader->setFallbackAutoloader(true);

Typically, you will use the version of Zend Framework that the autoloader you instantiate came with. However, when developing a project, it's often useful to track specific versions, major or minor branches, or just the latest version. Zend_Loader_Autoloader, as of version 1.10, offers some features to help manage this task.

Imagine the following scenario:

The autoloader allows you to do this with the method setZfPath(). This method takes two arguments, a path to a set of Zend Framework installations, and a version to use. Once invoked, it prepends a path to the include_path pointing to the appropriate Zend Framework installation library.

The directory you specify as your path should have a tree such as the following:

ZendFramework/
|-- 1.9.2/
|   |-- library/
|-- ZendFramework-1.9.1-minimal/
|   |-- library/
|-- 1.8.4PL1/
|   |-- library/
|-- 1.8.4/
|   |-- library/
|-- ZendFramework-1.8.3/
|   |-- library/
|-- 1.7.8/
|   |-- library/
|-- 1.7.7/
|   |-- library/
|-- 1.7.6/
|   |-- library/

(where path points to the directory "ZendFramework" in the above example)

Note that each subdirectory should contain the directory library, which contains the actual Zend Framework library code. The individual subdirectory names may be version numbers, or simply be the untarred contents of a standard Zend Framework distribution tarball/zipfile.

Now, let's address the use cases. In the first use case, in development, we want to track the latest source install. We can do that by passing "latest" as the version:

$autoloader->setZfPath($path, 'latest');

In the example from above, this will map to the directory ZendFramework/1.9.2/library/; you can verify this by checking the return value of getZfPath().

In the second situation, for quality assurance, let's say we want to pin to the 1.8 minor release, using the latest install you have for that release. You can do so as follows:

$autoloader->setZfPath($path, '1.8');

In this case, it will find the directory ZendFramework/1.8.4PL1/library/.

In the final case, for production, we'll pin to a specific version -- 1.7.7, since that was what was available when Quality Assurance tested prior to our release.

$autoloader->setZfPath($path, '1.7.7');

Predictably, it finds the directory ZendFramework/1.7.7/library/.

You can also specify these values in the configuration file you use with Zend_Application. To do so, you'd specify the following information:

[production]
autoloaderZfPath = "path/to/ZendFramework"
autoloaderZfVersion = "1.7.7"

[qa]
autoloaderZfVersion = "1.8"

[development]
autoloaderZfVersion = "latest"

Note the different environment sections, and the different version specified in each environment; these factors will allow Zend_Application to configure the autoloader appropriately.

Besides being able to specify arbitrary callbacks as autoloaders, Zend Framework also defines an interface autoloading classes may imlement, Zend_Loader_Autoloader_Interface:

interface Zend_Loader_Autoloader_Interface
{
    public function autoload($class);
}

When using this interface, you can simply pass a class instance to Zend_Loader_Autoloader's pushAutoloader() and unshiftAutoloader() methods:

// Assume Foo_Autoloader implements Zend_Loader_Autoloader_Interface:
$foo = new Foo_Autoloader();

$autoloader->pushAutoloader($foo, 'Foo_');

Below, please find a guide to the methods available in Zend_Loader_Autoloader.