PHP spl_autoload

Question

i dont really get the docs for spl_autoload

bool spl_autoload_register  ([ callback $autoload_function  ] )

from my understanding, it will try to run functions registered when php comes across a class not loaded already. so example,

public function autoload() {
    require ('nonLoadedClass.php');
}
spl_autoload_register(autoload);
$x = new nonLoadedClass();

will cause the require to run? so i can also register many autoload functions?

public function autoloadXXX() {...}
public function autoloadYYY() {...}
public function autoloadZZZ() {...}
spl_autoload_register('autoloadXXX');
spl_autoload_register('autoloadYYY');
spl_autoload_register('autoloadZZZ');

in the case of doctrine,

require_once(dirname(__FILE__) . '/lib/vendor/doctrine/Doctrine.php');
spl_autoload_register(array('Doctrine', 'autoload'));

an array is passed, so i guess it will try to run the autoload function within the Doctrine class (which was required)?

Answer 1

spl_autoloader_register registers a callback function/method, that will be called when your code is trying to use a not-known class.

A callback function can be described in several ways :

• a simple function name : 'my_function'
• a static method of a class : array('MyClass', 'myMethod')
• a method of an instance of a class : array($myObject, 'myMethod')

In the case of Doctrine, it seems to be the second solution : if a class that PHP doesn't know is used, the autoloader will call Doctrine::autoload, passing it the class name as a parameter.

so i can also register many autoload functions?

Yes, you can, with spl_autoload_register :

If there must be multiple autoload functions, spl_autoload_register() allows for this. It effectively creates a queue of autoload functions, and runs through each of them in the order they are defined.

But we don't generally define one autoloading function/method for each class we have ; that would be quite inefficient, I suppose.

Instead, we use the class-name, which is received by the autoloading function, to decide which file should be included.

For instance, an autoload function might look like this :

function my_autoloader($className)
{
    require LIBRARY_PATH . '/' . $className . '.php';
}

The trick being that if your files are named after the classes they contain, it immediatly becomes much easier ;-)

This is why classes are often named using the PEAR convention : My_Class_Name maps to the file My/Class/Name.php