Source code for: http://baylorrae.com/lazy-loading-with-php/

huck_autoloader.php

<?php

// Allows multiple __autoload stacks
// and keeps autoloader in Huck class
spl_autoload_register(array('Huck', 'autoload'));

class Huck {

    public static function autoload($class_name) {
        if( substr($class_name, 0, 5) === 'Huck_' ) {

            $file = dirname(__FILE__) . '/' . substr($class_name, 5) . '.php';
            if( file_exists($file) )
                require_once $file;
        }
    }

}
?>

the_syntax.php

<?php

function __autoload($class_name) {

  // looks for 'classes/user.php';
  $file = 'classes/' . strtolower($class_name) . '.php';
  if( file_exists($file) )
    require_once $file;
}

/*
    Because the User class has not been included on this page
    PHP will run `__autoload` and try to include it automatically
*/
$user = new User;

// do stuff with $user

?>