ServiceLocator in PHP

example.php

<?php

abstract class ServiceLocator
{
	protected static $locator;
	
	public static function load(ServiceLocator $locator)
	{
		self::$locator = $locator;
	}
	
	public static function locator()
	{
		return self::$locator;
	}
}

interface DAOServiceLocator
{
	public function db();
}

class Db
{
	public function connect()
	{
		return 'connected';
	}
}

class DAOLocator extends ServiceLocator implements DAOServiceLocator
{
	public function db()
	{
		return new Db();
	}
}

class DAO
{
	public function listAll()
	{
		echo ServiceLocator::locator()->db()->connect();
	}
}

ServiceLocator::load(new DAOLocator());

$dao = new DAO();
$dao->listAll();