Example of php singleton pattern

/**
* by bbs.it-home.org
* 2012-12-26
*/
class Mysql{
//This attribute is used to save the instance
private static $conn;
//The constructor is private, Prevent the creation of objects
private function __construct(){
$this->conn = mysql_connect('localhost','root','');
}
//Create a method for instantiating objects
public static function getInstance(){
if(!(self::$conn instanceof self)){
self::$conn = new self;
}
return self::$conn;
}
//Prevent the object from being copied
public function __clone(){
trigger_error('Clone is not allowed!');
}
}
//You can only get the instance in this way, not new and clone
$mysql = Mysql:: getInstance();
?>