The StandardAutoloader
Overview
Zend_Loader_StandardAutoloader is designed as a » PSR-0-compliant
autoloader. It assumes a 1:1 mapping of the namespace+classname to the filesystem,
wherein namespace separators and underscores are translated to directory separators. A
simple statement that illustrates how resolution works is as follows:
Previous incarnations of PSR-0-compliant autoloaders in Zend Framework have relied upon
the include_path for file lookups. This has led to a number of
issues:
-
Due to the use of include, if the file is not
found, a warning is raised -- even if another autoloader is capable of resolving
the class later.
-
Documenting how to setup the include_path has proven to be
a difficult concept to convey.
-
If multiple Zend Framework installations exist on the
include_path, the first one on the path wins -- even if that
was not the one the developer intended.
To solve these problems, the StandardAutoloader by default
requires that you explicitly register namespace/path pairs (or vendor prefix/path
pairs), and will only load a file if it exists within the given path. Multiple pairs may
be provided.
As a measure of last resort, you may also use the
StandardAutoloader as a "fallback" autoloader -- one that will
look for classes of any namespace or vendor prefix on the
include_path. This practice is not recommended, however, due to
performance implications.
Finally, as with all autoloaders in Zend Framework, the
StandardAutoloader is capable of registering itself with PHP's
SPL autoloader registry.
Note: Vocabulary: Namespaces vs. Vendor Prefixes
In terms of autloading, a "namespace" corresponds to PHP's own definition of
namespaces in PHP versions 5.3 and above.
A "vendor prefix" refers to the practice, popularized in PHP versions prior to 5.3,
of providing a pseudo-namespace in the form of underscore-separated words in class
names. As an example, the class Phly_Couch_Document uses a
vendor prefix of "Phly", and a component prefix of "Phly_Couch" -- but it is a class
sitting in the global namespace within PHP 5.3.
The StandardAutoloader is capable of loading either
namespaced or vendor prefixed class names, but treats them separately when
attempting to match them to an appropriate path.
Quick Start
Basic use of the StandardAutoloader requires simply registering
namespace/path pairs. This can either be done at instantiation, or via explicit method
calls after the object has been initialized. Calling register()
will register the autoloader with the SPL autoloader registry.
By default, the class will register the "Zend" namespace to the directory above where
its own classfile is located on the filesystem.
Example #1 Manual Configuration
// This example assumes ZF is on your include_path.
// You could also load the autoloader class from a path relative to the
// current script, or via an absolute path.
require_once 'Zend/Loader/StandardAutoloader.php';
$loader = new Zend_Loader_StandardAutoloader();
// Register the "Phly" namespace:
$loader->registerNamespace('Phly', APPLICATION_PATH . '/../library/Phly');
// Register the "Scapi" vendor prefix:
$loader->registerPrefix('Scapi', APPLICATION_PATH . '/../library/Scapi');
// Optionally, specify the autoloader as a "fallback" autoloader;
// this is not recommended.
$loader->setFallbackAutoloader(true);
// Register with spl_autoload:
$loader->register();
Example #2 Configuration at Instantiation
The StandardAutoloader may also be configured at
instantiation. Please note:
The following is equivalent to the previous example.
require_once 'Zend/Loader/StandardAutoloader.php';
$loader = new Zend_Loader_StandardAutoloader (array(
'Phly' => APPLICATION_PATH . '/../library/Phly',
),
'Scapi' => APPLICATION_PATH . '/../library/Scapi',
),
'fallback_autoloader' => true,
));
// Register with spl_autoload:
$loader->register();
Configuration Options
The StandardAutoloader defines the following options.
StandardAutoloader Options
-
- namespaces
-
An associative array of namespace/path pairs. The path should be an absolute
path or path relative to the calling script, and contain only classes that
live in that namespace (or its subnamespaces). By default, the "Zend"
namespace is registered, pointing to the arent directory of the file
defining the StandardAutoloader.
-
- prefixes
-
An associative array of vendor prefix/path pairs. The path should be an absolute
path or path relative to the calling script, and contain only classes that
begin with the provided vendor prefix.
-
- fallback_autoloader
-
A boolean value indicating whether or not this instance should act as a
"fallback" autoloader (i.e., look for classes of any namespace or vendor
prefix on the include_path). By default,
false.
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