A factory that remembers

dummy_classes.php

<?php

/**
 * @property int $id
 * @property string $class_name
 */
abstract class root {
	/**
	 * the identifier of this object
	 * @var int
	 */
	protected $id = null;
	/**
	 *
	 * @var array
	 */
	protected $data = array();
	/**
	 *
	 * @param int $id
	 */
	public function __construct( $id ) {
		$this->data['id'] = 
				$this->id =
				$id;
	}
	/**
	 * Set a value for this object
	 * @param stirng $var
	 * @param mixed $value
	 */
	public function __set($var, $value) {
		$var = strtolower($var);
		if(in_array($var, array('id', 'class_name'))) {
			throw new Exception('You can\'t set that!');
		}
		$this->data[$var] = $value;
	}
	/**
	 * Get a value from this object
	 * @param string $var
	 * @return mixed
	 */
	public function __get($var) {
		$var = strtolower($var);
		switch($var){
			case 'class_name':
				return $this->__toString();
				break;
			default:
				return isset($this->data[$var])? $this->data[$var]:null;
				break;
		}
	}
	public function __toString(){
		return get_class($this);
	}
}

/**
 * @property string $name
 */
class User extends root {
	public function __construct( $id ) {
		parent::__construct($id);
	}
}

factory.class.php

<?php

class factory {
	/**
	 * Hold all of the items in the factory
	 * @var array
	 */
	protected static $created = array();
	/**
	 * Create/Load an object from the factory
	 * @param string $className
	 * @param int $id
	 * @return root
	 */
	public static function Create($className, $id=null ) {
		$className = strtolower($className);
		if(!isset(self::$created[$className][$id])) {
			self::$created[$className][$id] = new $className($id);
		}
		return self::$created[$className][$id];
	}
	/**
	 * Load an object from the factory
	 * @param string $className the object's class
	 * @param int $id the id of the object you are loading
	 * @return root or null
	 */
	public static function Load($className, $id ) {
		$className = strtolower($className);
		return (isset(self::$created[$className][$id]))? self::$created[$className][$id]:null;
	}
	/**
	 * Add an object to the factory, has no effect if the object is already part of the factory
	 * @param string $className
	 * @param object $class
	 */
	public static function Add(root &$class) {
		$className = strtolower($class->class_name);
		if(!isset(self::$created[$className][$class->id])) {
			self::$created[$className][$class->id] = &$class;
		}
	}
	/**
	 * Destroy an instance of something in the factory and the object itself
	 * @param root $class the class being destroyed
	 */
	public static function Destroy(root &$class){
		$className = strtolower($class->class_name);
		$id = $class->id;
		unset(self::$created[$className][$id]);
		$class = null;
	}
}

factory_test.php

<?php

require 'dummy_classes.php';
require 'factory.class.php';

/**
 * @var User
 */
$u1 = factory::Create( 'User', 1 );
/**
 * copy of $u1
 * @var User
 */
$u2 = factory::Create( 'User', 1 );
$u1->name = 'Jack';
$u2->name = 'Sally';
/**
 * @var User
 */
$u3 = factory::Create( 'User', 2 );
$u3->name = 'Jim';


/**
 * @var User
 */
$u4 = new User(3);
$u4->name = 'Doug';
factory::Add($u4);

/**
 * copy of $u4
 * @var User
 */
$u5 = factory::Load('User', 3);


///should be the same
echo $u1->name . PHP_EOL; // #=>Sally
echo $u2->name . PHP_EOL; // #=>Sally
///should be by itself
echo $u3->name . PHP_EOL; // #=>Jim
///should be the same
echo $u4->name . PHP_EOL; // #=>Doug
echo $u5->name . PHP_EOL; // #=>Doug


factory::Destroy($u3);
var_dump($u3); // #=> null
$u3 = factory::Load('User', 2);
var_dump($u3); // #=> null

An implementation of a factory, includes add, create, destroy, load functions.