类的自动加载

在编写面向对象（OOP） 程序时，很多开发者为每个类新建一个 PHP 文件。 这会带来一个烦恼：每个脚本的开头，都需要包含（include）一个长长的列表（每个类都有个文件）。

在 PHP 5 中，已经不再需要这样了。 spl_autoload_register() 函数可以注册任意数量的自动加载器，当使用尚未被定义的类（class）和接口（interface）时自动去加载。通过注册自动加载器，脚本引擎在 PHP 出错失败前有了最后一个机会加载所需的类。

Tip

尽管 __autoload() 函数也能自动加载类和接口，但更建议使用 spl_autoload_register() 函数。 spl_autoload_register() 提供了一种更加灵活的方式来实现类的自动加载（同一个应用中，可以支持任意数量的加载器，比如第三方库中的）。因此，不再建议使用 __autoload() 函数，在以后的版本中它可能被弃用。

Note:

在 PHP 5.3 之前，__autoload 函数抛出的异常不能被 catch 语句块捕获并会导致一个致命错误（Fatal Error）。 自 PHP 5.3 起，能够 thrown 自定义的异常（Exception），随后自定义异常类即可使用。 __autoload 函数可以递归的自动加载自定义异常类。

Note:

自动加载不可用于 PHP 的 CLI 交互模式。

Note:

如果类名比如被用于 call_user_func()，则它可能包含一些危险的字符，比如 ../。 建议您在这样的函数中不要使用用户的输入，起码需要在 __autoload() 时验证下输入。

Example #1 自动加载示例

本例尝试分别从 MyClass1.php 和 MyClass2.php 文件中加载 MyClass1 和 MyClass2 类。

<?php
spl_autoload_register(function ($class_name) {
    require_once $class_name . '.php';
});

$obj  = new MyClass1();
$obj2 = new MyClass2();
?>

Example #2 另一个例子

本例尝试加载接口 ITest。

<?php

spl_autoload_register(function ($name) {
    var_dump($name);
});

class Foo implements ITest {
}

/*
string(5) "ITest"

Fatal error: Interface 'ITest' not found in ...
*/
?>

Example #3 自动加载在 PHP 5.3.0+ 中的异常处理

本例抛出一个异常并在 try/catch 语句块中演示。

<?php
spl_autoload_register(function ($name) {
    echo "Want to load $name.\n";
    throw new Exception("Unable to load $name.");
});

try {
    $obj = new NonLoadableClass();
} catch (Exception $e) {
    echo $e->getMessage(), "\n";
}
?>

以上例程会输出：

Want to load NonLoadableClass.
Unable to load NonLoadableClass.

Example #4 自动加载在 PHP 5.3.0+ 中的异常处理 - 没有自定义异常机制

本例将一个异常抛给不存在的自定义异常处理函数。

<?php
spl_autoload_register(function ($name) {
    echo "Want to load $name.\n";
    throw new MissingException("Unable to load $name.");
});

try {
    $obj = new NonLoadableClass();
} catch (Exception $e) {
    echo $e->getMessage(), "\n";
}
?>

以上例程会输出：

Want to load NonLoadableClass.
Want to load MissingException.

Fatal error: Class 'MissingException' not found in testMissingException.php on line 4

参见

User Contributed Notes

str at maphpia dot com 01-Dec-2016 07:36
This is my autoloader for my PSR-4 clases. I prefer to use composer's autoloader, but this works for legacy projects that can't use composer.

<?php
/**
 * Simple autoloader, so we don't need Composer just for this.
 */
class Autoloader
{
    public static function register()
    {
        spl_autoload_register(function ($class) {
            $file = str_replace('\\', DIRECTORY_SEPARATOR, $class).'.php';
            if (file_exists($file)) {
                require $file;
                return true;
            }
            return false;
        });
    }
}
Autoloader::register();
oliver dot strevel at gmail dot com 14-Jul-2014 12:50
My autoloader function:

<?php

/**
 * Funcion de autocarga de clases para php
 * Se realiza la busqueda directamente sobre la raiz de la carpeta lib con el prefijo '.class.php'
 */
function __autoload( $class_name )
{
    $invalidChars = array(
        '.', '\\', '/', ':', '*', '?', '"', '<', '>', "'", '|'
    );
   
    $class_name = str_replace($invalidChars, '', $class_name);
   
    $extension_prefix = '.class.php';
   
    if( !@include_once $class_name . $extension_prefix )
    {
        $path = 'lib'; // In this dir the function will search
       
        foreach( new DirectoryIterator($path) as $file )
        {
            if($file->isDot()) { continue; }
           
            if($file->isDir())
            {
                $file = $path . DIRECTORY_SEPARATOR . $file->getFilename() . DIRECTORY_SEPARATOR . $class_name . $extension_prefix;   
               
                if(file_exists($file)) {
                    include_once $file;
                }
            }
        }   
    }
    if (!class_exists($class_name, false) || !interface_exists($class_name, false)) {
        // return || Some tracking error task..
    }
}
?>
norwood at computer dot org 11-Jan-2014 04:12
Autoloaders & Namespaces: The effective namespace of an autoloaded file must match that of its original reference; just  finding and loading the file isn't enough. (I know, seems obvious now, but...)

My namespaces may serve as hints to locations within the file system, and I tried to be cute:
     If a class (file) wasn't found where it was expected, my autoloader also looked in an alternate location. This worked fine, except that the alternate's own qualified namespace was thus slightly different (reflecting where *it* lived). So although the desired class was ultimately loaded (name and all), the original caller's reference remained unsatisfied because of the namespace discrepancy (as it should, really), but it was subtle.

Of course, this scheme works fine within the same namespace (explicit or not).

And kudos to the autoload devs for anticipating what could have been an endless autoload loop.
pier4r 31-Dec-2013 02:46
Just a small autoload class (that works if you use corretly names, namespaces, uses and so on) found elsewhere with a small modification for linux:

<?php
//from http://www.phpfreaks.com / tutorial / oo - php - part - 1 - oop - in - full - effect
function __autoload($className)  {
  var_dump($className);
  $file = str_replace('\\', DIRECTORY_SEPARATOR, $className) . '.php';
  var_dump($file);

  var_dump(file_exists($file));
  if (!file_exists($file)) {
    return false;
  }
  else {
    require $file;
    return true;
  }
}
?>
julian at jxmallett dot com 15-Dec-2013 11:41
The tip to use spl_autoload_register() instead of __autoload() should be taken seriously. It seems that __autoload() doesn't always get called when calling an unloaded class within a class, eg:

<?php
class MyClass {
    public static function doStuff() {
        //do some stuff
        $a = MyOtherClass::otherStuff();
    }
}
?>

Code similar to that gave me a 'class not found' error when using __autoload(). Using spl_autoload_register() with the exact same autoload function fixed the problem.
tlang at halsoft dot com 14-Feb-2013 09:56
This page states that autoloading does not work when PHP is used in CLI mode but a simple test seems to contradict this.

Create a file /tmp/Foo.php containing:

<?php
class Foo {
    public function __construct() {
        echo "Inside the Foo constructor\n";
    }
}
?>

Create a script (NOT in /tmp) containing:

<?php

function test_autoload($class) {
    require_once '/tmp/'.$class.'.php';
}

spl_autoload_register('test_autoload');
$foo = new Foo();
?>

Execute the script on the command line. The echo statement in the constructor produces output to STDOUT.

This also works with __autoload

<?php

function __autoload($class) {
    require_once '/tmp/'.$class.'.php';
}

$foo = new Foo();
?>
qfox at ya dot ru 16-Nov-2011 02:48
More simpler example of using spl_autoload_register in 5.3:
<?php
spl_autoload_register(function($classname) /* usign $app */ {
  # ... your logic to include classes here
});
?>
fka at fatihkadirakin dot com 31-Jul-2010 06:16
Or you can use this, without using any "require/include":

<?php
class autoloader {

    public static $loader;

    public static function init()
    {
        if (self::$loader == NULL)
            self::$loader = new self();

        return self::$loader;
    }

    public function __construct()
    {
        spl_autoload_register(array($this,'model'));
        spl_autoload_register(array($this,'helper'));
        spl_autoload_register(array($this,'controller'));
        spl_autoload_register(array($this,'library'));
    }

    public function library($class)
    {
        set_include_path(get_include_path().PATH_SEPARATOR.'/lib/');
        spl_autoload_extensions('.library.php');
        spl_autoload($class);
    }

    public function controller($class)
    {
        $class = preg_replace('/_controller$/ui','',$class);
       
        set_include_path(get_include_path().PATH_SEPARATOR.'/controller/');
        spl_autoload_extensions('.controller.php');
        spl_autoload($class);
    }

    public function model($class)
    {
        $class = preg_replace('/_model$/ui','',$class);
       
        set_include_path(get_include_path().PATH_SEPARATOR.'/model/');
        spl_autoload_extensions('.model.php');
        spl_autoload($class);
    }

    public function helper($class)
    {
        $class = preg_replace('/_helper$/ui','',$class);

        set_include_path(get_include_path().PATH_SEPARATOR.'/helper/');
        spl_autoload_extensions('.helper.php');
        spl_autoload($class);
    }

}

//call
autoloader::init();
?>
ej at campbell dot name 03-Apr-2010 11:21
You don't need exceptions to figure out if a class can be autoloaded. This is much simpler.

<?php
//Define autoloader
function __autoload($className) {
      if (file_exists($className . '.php')) {
          require_once $className . '.php';
          return true;
      }
      return false;
}

function canClassBeAutloaded($className) {
      return class_exists($className);
}
?>
tom at r dot je 11-Mar-2010 03:30
To find out whether a class can be autoloaded, you can use autoload in this way:

<?php
//Define autoloader
function __autoload($className) {
    if (file_exists($className . '.php')) require $className . '.php';
    else throw new Exception('Class "' . $className . '" could not be autoloaded');
}

function canClassBeAutloaded($className) {
    try {
        class_exists($className);
        return true;
    }
    catch (Exception $e) {
        return false;
    }
}
?>
Anonymous 08-Feb-2010 03:35
It's worth to mention, if your operating system is case-sensitive you need to name your file with same case as in source code eg. MyClass.php instead of myclass.php
khan at swcombine dot com 05-Nov-2009 05:38
As an addendum to #91119 I would suggest adding class_exists() into that solution. I've just implemented autoloading based on the code provided there and ran into a problem where a file had the same name as a class, existed in the directory structure prior to the file that had the actual class and as a result was being included first and resulting in a 'class not found' error.

<?php
if(file_exists($path)) {
    require_once $path;
    if(class_exists($class_name)) {
        return;
    }
}
?>
Peminator 07-Jul-2009 07:01
My idea for autoloading FUNCTIONS however only in a weird way :

<?php
function ex($parms)
{
   $argvar = func_get_args();
   $func = $argvar[0];
   $funcargs = array_slice($argvar,1);
  
if (function_exists($func))
   {
   $returnvalue = call_user_func_array($func,$funcargs);
   }
else
   {
   $funcpath = "scripts/".$func.".php";
   require_once($funcpath);
  
   if (function_exists($func))
      {
      $returnvalue = call_user_func_array($func,$funcargs);
      } 
   else
      {
         die "SORRY  $func IS NOT USABLE";
      }
   }
 
// return returned value :-)
return $returnvalue;
}
?>

USAGE EXAMPLE:
must be caled using the X function giving the real function as first parameter, like:
$result = ex("add",1,2);
// returns 3 if add function defined in add.php sums the first and second parameter..
roman dot drapeko at gmail dot com 05-Apr-2009 04:33
Hi there,

I have developed a small script, that can scan recursively folders and files ang generate array of associations between classes/interfaces and their locations. It accepts several incoming parameters and it's very simple to use.

An example of generated array is shown bellow.

<?php

    $autoload_list = array (
      'classes' => array (
        'A' => array ('path' => 'Project/Classes/Children/A.php',
          'extends' => array (), 'implements' => array ('I1')),
        'C' => array ('path' => 'Project/Classes/C.php',
          'extends' => array ('B'), 'implements' => array ('I1', 'I3')),
      ),
      'interfaces' => array (
        'I2' => array ('path' => 'Project/Interfaces/blablabla.php', 'extends' => array ('I1')),
        'I1' => array ('path' => 'Project/Interfaces/I1.php', 'extends' => array ()),
      ),
    );
?>

When you know names and their locations, you know everything to load these classes.

It uses regular expressions to identify if class/interfaces is located in the current file.

I tried to post the code, but it's very long. You can download the script from http://wp.drapeko.com/store/php-autoloading-files/.
claude dot pache at gmail dot com 11-Mar-2009 07:04
About static classes that need initialisation before use (problem discussed by adam at greatbigmassive dot net and kalkamar at web dot de below).

Simple problems have often simple solutions. Here is my approach:

First, my __autoload function is very simple:
<?php
function __autoload ($class_name)
{
    if (preg_match('|^\w+$|', $class_name))
        include "./packages/$class_name.php";
}
?>
(The "if/preg_match" line is just a simple yet robust security check. Moreover I use "include" and not "require"/"require_once", so that if the file is not found, the __autoload function does nothing, and my script dies eventually with a meaningful "Class 'foo' not found"  fatal error.)

Now, when I define a class "foo" which requires initialisation before use, I just write the initialisation code after the definition of the class in the file "packages/foo.php":

<?php
/** Content of file "packages/foo.php" **/
class foo
{
    /* definition of the class is found here */
}

/* initialisation code of the class is found here. */

/** End of file "packages/foo.php" **/
?>

That's it. No need for an <? init() ?> or a <? __construct() ?> method.
jarret dot minkler at gmail dot com 07-Mar-2009 10:55
You should not have to use require_once inside the autoloader, as if the class is not found it wouldn't be trying to look for it by using the autoloader.

Just use require(), which will be better on performance as well as it does not have to check if it is unique.
pinochet dot pl at gmail dot com 04-Jan-2009 01:11
To use autoload function with namespaces you should remember to define it in main scope in "\" namespace.
zachera 31-Dec-2008 04:55
I found out a neat way to centralize one single class which will give accessibility to other classes.  I also added a parameter to the __construct method which would be an array of classes you want loaded.  This isn't completely necessary, but it will stop "excessive memory" if you're loading a bunch of unused classes.

<?php
class Bot {
    private $classes = array (
        'Socket' => "connection/class.Socket.php",
        'Input'  => "io/class.Input.php",
        'Output' => "io/class.Output.php",
        'Parse'  => "io/parse/class.Parse.php"
    );
    public $Socket, $Input, $Output, $Parse; // Accessible by other classes

    public function __construct($load=false){
        if(is_array($load)){
            foreach($load as $class){
                if(isset($this->classes[$class])){
                    require($this->classes[$class]);
                    $this->$class = new $class($this);
                }
            }
        } else {
            foreach($this->classes as $class => $path){
                require($path);
                $this->$class = new $class($this);
            }
        }
    }
}
?>
kalkamar at web dot de 07-Oct-2008 10:23
Because static classes have no constructor I use this to initialize such classes.
The function init will (if available) be called when you first use the class.
The class must not be included before, otherwise the init-function wont be called as autoloading is not used.

<?php
function __autoload($class_name)
{
    require_once(CLASSES_PATH.$class_name.'.cls.php');
    if(method_exists($class_name,'init'))
        call_user_func(array($class_name,'init'));
    return true;
}
?>

I use it for example to establish the mysql-connection on demand.

It is also possilbe do add a destructor by adding this lines to the function:
<?php
if(method_exists($class_name,'destruct'))
    register_shutdown_function(array($class_name,'destruct'));
?>
jbarker at erepublic dot com 17-Sep-2008 08:34
In a subclass, I was trying to call an overridden parent method with an arbitrary number of arguments:

<?php
call_user_func_array(array('parent', 'someNonStaticMethod'), $args);
?>

It turns out this triggers an E_STRICT level warning. So I changed to this:

<?php
call_user_func_array(array($this, 'parent::someNonStaticMethod'), $args);
?>

This doesn't trigger any warnings, but it has the undesirable (if not downright buggy) effect of calling my __autoload() function with the argument 'parent'. I had to modify __autoload() to handle this special situation:

<?php
function __autoload($cls)
{
    if ('parent' != $cls)
    {
        require("class.$cls.php");
    }
}
?>

Tested on Linux with PHP 5.1.6 and 5.2.5.
matias dot cohen at gmail dot com 01-Aug-2008 04:33
Another way of throwing exceptions inside an __autoload() function:
<?php

function myExceptionHandler($e) {
    // Add code here
}

set_exception_handler('myExceptionHandler');

function __autoload($class) {
    if (class_exists($class, false) || interface_exists($class, false)) {
        return;   
    }
    try {
        @require_once('path/to/' . $class . '.php');
        if (!class_exists($class, false) || !interface_exists($class, false)) {
            throw new Exception('Class ' . $class . ' not found');
        }
    }
    catch (Exception $e) {

        myExceptionHandler($e);
    }
}

?>
chris (at) xeneco (dot) co (dot) uk 04-Jul-2008 06:21
I'm very taken with the autoload function, and thought I would share with you my implementation of it:
<?php
function __autoload($class_name) {

    //my settings class is a singleton instance that has parsed an ini file containing the locations of all classes
    $settings = Settings::Load();
    $classes = $settings->getSettings('classes');

    $path = $classes[$class_name];
   
    if(file_exists($path)) {
        require_once($path);
        return true;
    } else {
        clearstatcache();
        $classes = $settings->ReLoadSettings();
        $path = $classes['classes'][$class_name];
    }
       
    if(file_exists($path)) {
        require_once($path);
        return true;
    } else {
        die("The requested library,".$class_name.", could not be found at ".$classes[$class_name][$i].". Please check your ini file");
    }
}
?>
james dot dot dot dunmore at gmail dot com 18-Apr-2008 04:43
Andrew: 03-Nov-2006 12:26

That seems a bit messy to me, this is a bit neater:
<?php
    function __autoload($class_name)
    {
        //class directories
        $directorys = array(
            'classes/',
            'classes/otherclasses/',
            'classes2/',
            'module1/classes/'
        );
       
        //for each directory
        foreach($directorys as $directory)
        {
            //see if the file exsists
            if(file_exists($directory.$class_name . '.php'))
            {
                require_once($directory.$class_name . '.php');
                //only require the class once, so quit after to save effort (if you got more, then name them something else
                return;
            }           
        }
    }
muratyaman at gmail dot com 28-Jan-2008 07:57
__autoload() function can be very useful to optimize your code esp. when you have so many classes.

Unlike class extensions, optional parameters with class restrictions may not load your class.

<?php
class bClass{
  function fun($p1, aClass $p2=NULL){
    //do something
  }
}

//depending on the usage
$b = new bClass();
$b->fun('No!');//this will not load class file for aClass
$b->fun('Really?', new aClass('Yes!'));//this will

?>

So, it's very encouraging to use classes everywhere!
Even encapsulating your functions inside simple classes to use like static modules, will help a lot!

Let's say, you have <b>50k</b> lines of code inside <b>100</b> classes/files.. If you need a simple task to do very quickly, you should not be loading all of those files, except the ones you need.

Though, it may be dangerous on some cases regarding the dependencies, load order, etc. Carefully design your classes.
richard [at ] xanox [dot] net 05-Dec-2007 07:46
I've made this little script here which looks in a dir, and loads all the classed, and includes their files.

$myDirectory = opendir("required/classes");

// get each entry
while($entryName = readdir($myDirectory)) {
    $dirArray[] = $entryName;
}

// close directory
closedir($myDirectory);

//    count elements in array
$indexCount    = count($dirArray);
sort($dirArray);

for($index=0; $index < $indexCount; $index++) {
    if($dirArray[$index] != '.' AND $dirArray[$index] != '..') {
        include("required/classes/$dirArray[$index]");
        $classname = strtolower($dirArray[$index]);
        $classname = str_replace('.php','',$classname);
        $classinit = str_replace('.php','',$dirArray[$index]);

        $$classname = new $classinit;
    }
}
rojoca 04-Oct-2007 08:38
Be careful when using eval (as always) in __autoload. The following:

<?php

echo 'Start->';

function __autoload($class) {
    eval('class ' . $class . ' {};');
}

$class = 'Class1{}; echo "uh oh"; class Class2';

$obj = new $class;

echo 'end';
?>

outputs:

Start->uh oh

You can use preg_replace to clean up $class to prevent executing abitrary code but in this case you won't be able to throw a catchable exception and your script will end with a fatal error.
christian.reinecke at web.de 23-Sep-2007 09:28
do not use is_subclass_of() in your __autoload() function to identify a class type and thereby its path (f.e exceptions). is_subclass_of() needs to know the class, but you want to check BEFORE you include the class.
peter dot gooman at gmail dot com 17-Jun-2007 08:33
Before you start using __autload, remember that it holds no scope/namespace. This means that if you are depending on third party applications and they have an autoload function defined and so do you, your application will error.

To remedy this, everyone should look at the spl_autoload functions, eg: spl_autoload_register. This function allows more than one custom functions to be called through the default spl_autoload (default __autoload) handler.
david dot thalmann at gmail dot com 02-Feb-2007 07:19
Note to Ricos posting:
A lot of useless Coding. However, I improved the code, so now it will be able to find any folders ("." and ".." will not being tested... oO) and search as deep as possible. Now it will find CLASS_DIR/foo/bar.class.php also like CLASS_DIR/foo/bar/baz/buz/fii/and/so/on/class.php

Warning: This code will check ALL dirs who're "deeper" / "lower" than the class dir, so prevent deeply hidden files (or use just a few folders).

Improved Version:
<?php

// change this, if this code isn't "higher" than ALL classfiles
define("CLASS_DIR", dirname(__FILE__));

/**
 * autoload classes (no need to include them one by one)
 *
 * @uses classFolder()
 * @param $className string
 */
function __autoload($className) {
    $folder = classFolder($className);

    if($folder)
        require_once($folder.$className.".class.php");
}

/**
 * search for folders and subfolders with classes
 *
 * @param $className string
 * @param $sub string[optional]
 * @return string
 */
function classFolder($className, $sub = "/") {
    $dir = dir(CLASS_DIR.$sub);
   
    if(file_exists(CLASS_DIR.$sub.$className.".class.php"))
        return CLASS_DIR.$sub;

    while(false !== ($folder = $dir->read())) {
        if($folder != "." && $folder != "..") {
            if(is_dir(CLASS_DIR.$sub.$folder)) {
                $subFolder = classFolder($className, $sub.$folder."/");
               
                if($subFolder)
                    return $subFolder;
            }
        }
    }
    $dir->close();
    return false;
}

?>
Rico 04-Jan-2007 05:00
This autoload function searches for the class Location before requiring it. So there's no need of putting the classes all in one folder.

Requirements:
 - the subfolders must be at least 3 letters long
 - the filenames must be in the form CLASSNAME.class.php

Note:
 - in this example the main class folder is 'lib'

define('ROOT_DIR', dirname(__FILE__).'/');

function __autoload($className) {
    $folder=classFolder($className);
    if($folder) require_once($folder.'/'.$className.'.class.php');
}

function classFolder($className,$folder='lib') {
    $dir=dir(ROOT_DIR.$folder);
    if($folder=='lib' && file_exists(ROOT_DIR.$folder.'/'.$className.'.class.php')) return $folder;
    else {
        while (false!==($entry=$dir->read())) {
            $checkFolder=$folder.'/'.$entry;
            if(strlen($entry)>2) {
                if(is_dir(ROOT_DIR.$checkFolder)) {
                    if(file_exists(ROOT_DIR.$checkFolder.'/'.$className.'.class.php')) return $checkFolder;
                    else {
                        $subFolder=classFolder($className,$checkFolder);
                        if($subFolder) return $subFolder;
                    }
                }
            }
        }
    }
    $dir->close();
    return 0;
}
Chris Corbyn (chris AT w3style.co.uk) 08-Sep-2006 06:23
I'm sure this is needed by more than me.

My objective was to allow __autoload() to be easily extended in complex systems/frameworks where specific libraries etc may need loading differently but you don't want to hard-code little adjustments into your working __autoload() to allow this to happen.

Using a ServiceLocator object with some static methods and properties to allow loosely coupled locators to be attached to it you can swap/change and add to the functionality of your __autoload() at runtime.

The core stuff:
<?php

/**
 * Defines the methods any actual locators must implement
 * @package ServiceLocator
 * @author Chris Corbyn
 */
interface Locator
{
    /**
     * Inform of whether or not the given class can be found
     * @param string class
     * @return bool
     */
    public function canLocate($class);
    /**
     * Get the path to the class
     * @param string class
     * @return string
     */
    public function getPath($class);
}

/**
 * The main service locator.
 * Uses loosely coupled locators in order to operate
 * @package ServiceLocator
 * @author Chris Corbyn
 */
class ServiceLocator
{
    /**
     * Contains any attached service locators
     * @var array Locator
     */
    protected static $locators = array();
   
    /**
     * Attach a new type of locator
     * @param object Locator
     * @param string key
     */
    public static function attachLocator(Locator $locator, $key)
    {
        self::$locators[$key] = $locator;
    }
    /**
     * Remove a locator that's been added
     * @param string key
     * @return bool
     */
    public static function dropLocator($key)
    {
        if (self::isActiveLocator($key))
        {
            unset(self::$locators[$key]);
            return true;
        }
        else return false;
    }
    /**
     * Check if a locator is currently loaded
     * @param string key
     * @return bool
     */
    public static function isActiveLocator($key)
    {
        return array_key_exists($key, self::$locators);
    }
    /**
     * Load in the required service by asking all service locators
     * @param string class
     */
    public function load($class)
    {
        foreach (self::$locators as $key => $obj)
        {
            if ($obj->canLocate($class))
            {
                require_once $obj->getPath($class);
                if (class_exists($class)) return;
            }
        }
    }
}

/**
 * PHPs default __autload
 * Grabs an instance of ServiceLocator then runs it
 * @package ServiceLocator
 * @author Chris Corbyn
 * @param string class
 */
function __autoload($class)
{
    $locator = new ServiceLocator();
    $locator->load($class);
}

?>

An example Use Case:
<?php

require 'ServiceLocator.php';

//Define some sort of service locator to attach...
class PearLocator implements Locator
{
    protected $base = '.';
   
    public function __construct($directory='.')
    {
        $this->base = (string) $directory;
    }
   
    public function canLocate($class)
    {
        $path = $this->getPath($class);
        if (file_exists($path)) return true;
        else return false;
    }
   
    public function getPath($class)
    {
        return $this->base . '/' . str_replace('_', '/', $class) . '.php';
    }
}

// ... attach it ...
ServiceLocator::attachLocator(new PearLocator(), 'PEAR');

// ... and code away....
$foo = new Foo_Test();

?>
gonix 03-Aug-2006 06:39
in response to alexey at renatasystems dot org:

You may add ``global $somedata;`` before ``$somedata = 'Some data';`` and it should work as expected.

file bar.class.php:

<?php

global $somedata;
$somedata = 'Some data';    /* global scope in common way */

class bar {

   function __construct()  
   {  
       global $somedata;    /* reference to global scope variable */
     
       if ( isset($somedata) )
       {
           var_dump($somedata);
       }
       else
       {
           die('No data!');
       }
   }
}
?>

'common way':
<?php

require 'bar.class.php';

$foo = new bar();

?>

'__autoload way':
<?php

function __autoload($classname)
{
   require $classname . '.class.php';
}

$foo = new bar();

?>

Both 'comon way' and '__autoload way' should give same result:
string(9) "Some data"
alexey at renatasystems dot org 06-Jul-2006 12:15
While using an "autoloading" method you should pay attention to variables scope. Because of new file will be included INSIDE of magic function __autoload - all of declared in such file global scope variables will be only available within this function and nowhere else. This will cause strange behaviour in some cases. For example:

file bar.class.php:

<?php

$somedata = 'Some data';     /* global scope in common way */

class bar {

    function __construct()   
    {   
        global $somedata;    /* reference to global scope variable */
       
        if ( isset($somedata) )
        {
            var_dump($somedata);
        }
        else
        {
            die('No data!');
        }
    }
}
?>

Attempt to load this file in common way:

<?php

require 'bar.class.php';

$foo = new bar();

?>

this will output (as expected):

string(9) "Some data"

But in case of __autoload:

<?php

function __autoload($classname)
{
    require $classname . '.class.php';
}

$foo = new bar();

?>

you could expect that this script will return the same but no, it will return "No data!", because defenition of $somedata after requiring treats as local within user-defined function __autoload().
RQuadling at GMail dot com 08-Mar-2006 12:55
An issue I've had with using the __autoload function is getting it into the application.

You have to have the function included in every topmost script. This is a pain if the entire application is OOP and an "app" can be just a component of another "app".

A solution I've found is to use php.ini's auto_prepend_file setting.

Mine is set to ...

auto_prepend_file = auto_loader.php

The auto_loader.php script contains a single function. The __autoload() function.

The include_dir path IS examined to find this file, so you can just put it with the rest of your includable files.

A useful additional facility here is that you could log which classes are used by a script at runtime. Very useful if you have object factories and can't know the load at design time.

Also, assigning the uncaught exception handler and the error handlers in this file means your entire site WILL have some global protection without you having to deal with it on a script by script basis.

If you do not have access to the PHP.INI file, or you are running on a shared server, you may not be able to set this property. In those cases, you may be able to set the value using .htaccess. (NOTE: UNTESTED as I don't use Apache).

<IfModule mod_php5.c>
  php_value auto_prepend_file "auto_loader.php"
</IfModule>

You COULD therefore have a different set of rules per subdomain (if you have multiple subdomains, say, live, test, beta, devel) or whatever takes your fancy.

For more details on this see the "Description of core php.ini directives" (http://www.php.net/manual/en/ini.core.php)
dave60 /at/ gmail /dot/ com 29-Dec-2005 01:25
In reply to quetzalcoatl:

Generally, I would advise for each class to have it's own file, and hold nothing besides that class. Just define __autoload() in a/the infrastructure file -- a/the file that does the behavioral logic, and there should be no need to redefine it in a class' file.
me at mydomain dot com 11-Nov-2005 04:07
You can enable this behaviour for undefined classes while unserializing objects by setting the .ini-variable 'unserialize_callback_func' to '__autoload'.
petyo()architect . bg 30-Jan-2005 01:27
The following function may be useful if you want to simulate namespaces and autoloading behavior:

define ("CLASS_ROOT", '/classes/');
function __autoload ($className)
{
    require_once CLASS_ROOT.str_replace('_', '/', $className).'.class.php';
}

Then you will just have to use the folder structure and name the classes accordingly. If you want to have a class named Page, which will be in the pseudo namespace System.Web.UI, create a directory named System in /classes, then create Web, then UI, then name the class System_Web_UI_Page. Kind of long to type if you don't have autocomplete, but at least you will not have to manage the loading of all the classes' definitions.