# 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:

    $filename = str_replace(array('_', '\\'), DIRECTORY_SEPARATOR, $classname)
              . '.php';

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.

### 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.

### 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();

### Configuration at Instantiation

The `StandardAutoloader` may also be configured at instantiation. Please note:

- The argument passed may be either an array or a Traversable object (such as a `Zend_Config` object.

- The argument passed is also a valid argument for passing to the `setOptions()` method.

The following is equivalent to the previous example.

    require_once 'Zend/Loader/StandardAutoloader.php';
    $loader = new Zend_Loader_StandardAutoloader(array(
        'namespaces' => array(
            'Phly' => APPLICATION_PATH . '/../library/Phly',
        ),
        'prefixes' => array(
            '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`.

## Available Methods

### __construct

Initialize a new instance of the object
__construct
$options = null

#### Constructor

Takes an optional `$options` argument. This argument may be an associative array or Traversable object. If not null, the argument is passed to `setOptions()`.

### setOptions

Set object state based on provided options.
setOptions
$options

#### setOptions()

Takes an argument of either an associative array or Traversable object. Recognized keys are detailed under , with the following behaviors:

- The `namespaces` value will be passed to registerNamespaces().

- The `prefixes` value will be passed to registerPrefixes().

- The `fallback_autoloader` value will be passed to setFallbackAutoloader().

### setFallbackAutoloader

Enable/disable fallback autoloader status
setFallbackAutoloader
$flag

#### setFallbackAutoloader()

Takes a boolean flag indicating whether or not to act as a fallback autoloader when registered with the SPL autoloader.

### isFallbackAutoloader

Query fallback autoloader status
isFallbackAutoloader

#### isFallbackAutoloader()

Indicates whether or not this instance is flagged as a fallback autoloader.

### registerNamespace

Register a namespace with the autoloader
registerNamespace
$namespace, $directory

#### registerNamespace()

Register a namespace with the autoloader, pointing it to a specific directory on the filesystem for class resolution. For classes matching that initial namespace, the autoloader will then perform lookups within that directory.

### registerNamespaces

Register multiple namespaces with the autoloader
registerNamespaces
$namespaces

#### registerNamespaces()

Accepts either an array or Traversable object. It will then iterate through the argument, and pass each item to registerNamespace().

### registerPrefix

Register a vendor prefix with the autoloader.
registerPrefix
$prefix, $directory

#### registerPrefix()

Register a vendor prefix with the autoloader, pointing it to a specific directory on the filesystem for class resolution. For classes matching that initial vendor prefix, the autoloader will then perform lookups within that directory.

### registerPrefixes

Register many vendor prefixes with the autoloader
registerPrefixes
$prefixes

#### registerPrefixes()

Accepts either an array or Traversable object. It will then iterate through the argument, and pass each item to registerPrefix().

### autoload

Attempt to load a class.
autoload
$class

#### autoload()

Attempts to load the class specified. Returns a boolean `false` on failure, or a string indicating the class loaded on success.

### register

Register with spl_autoload.
register

#### register()

Registers the `autoload()` method of the current instance with `spl_autoload_register()`.

## Examples

Please review the examples in the quick start for usage.