<?

class Example

{

//The factory method

public static function factory($type)

{

if (include_once 'Drivers/' . $type . '.php'){

$classname = 'Driver_' . $type;

return new $classname;

}else{

throw new Exception ('Driver not found');

}}

}

<?

//Load a MySQL Driver

$mysql = Example::factory('MySQL');

//Load a SQLite Driver

$sqlite = Example::factory('SQLite');

<?

class Example

{

//Hold an instance of the class

private static $instance;

//A private constructor; prevents direct creation of object

private function __construct()

{

echo 'I am constructed';

}

//The singleton method

public static function singleton()

{

if (!isset(self::$instance)){

$c = __CLASS__;

self::$instance = new $c;

}

return self::$instance;

}

//Example method

public function bark()

{

echo 'Woof!';

}

//Prevent users to clone the instance

public function __clone()

{

trigger_error('Clone is not allowed.', E_USER_ERROR);

}}

<?

//This would fail because the constructor is private

$test = new Example;

//This will always retrieve a single instance of the class

$test = Example::singleton();

$test->bark();

//This will issue an E_USER_ERROR.

$test_clone = clone($test);