class factory{
  function __construct($name){
    if(file_exists('./'.$name.'.class.php')){
      return new $name;
    }else{
      die('not exist');
    }
  }
}

class instance{
  public $val = 10;
  private static $instance ;
  private function __construct(){}
  private function __clone(){}
  //设置为静态方法才可被类调用
  public static function getInstance(){
    /*if(!isset(self::$instance)){
      self::$instance = new self;
    }*/
    if(!isset(instance::$instance)){
      instance::$instance = new self;
    }
    return instance::$instance;
  }
}
$obj_one = instance::getInstance();
$obj_one->val = 20;
//clone可以调用__clone()克隆即new出一个新的的对象
//$obj_two = clone $obj_one;
$obj_two = instance::getInstance();
echo $obj_two->val;
echo '<p>';
var_dump($obj_one,$obj_two);

20
object(instance)[1]
 public 'val' => int 20
object(instance)[1]
 public 'val' => int 20

class mysqldb{
  private $arr = array(
    'port' => 3306,
    'host' => 'localhost',
    'username' => 'root',
    'passward' => 'root',
    'dbname' => 'instance',
    'charset' => 'utf8'
     );
  private $link;
  static $instance;
  private function __clone(){}
  private function __construct(){
    $this->link = mysql_connect($this->arr['host'],$this->arr['username'],$this->arr['passward']) or die(mysql_error());
    mysql_select_db($this->arr['dbname']) or die('db error');
    mysql_set_charset($this->arr['charset']);
  }
  static public function getInsance(){
    if(!isset(mysqldb::$instance)){
      mysqldb::$instance = new self;
    }
    return mysqldb::$instance;
  }
  public function query($sql){
    if($res = mysql_query($sql)){
      return $res;
    }return false;
  }
  //fetch one
  public function get_one($sql){
    $res = $this->query($sql);
    if($result = mysql_fetch_row($res)){
      return $result[0];
    }
  }
  //fetch row
  public function get_row($sql){
    $res = $this->query($sql);
    if($result = mysql_fetch_assoc($res)){
      return $result;
    }
    return false;
  }
  //fetch all
  public function get_all($sql){
    $res = $this->query($sql);
    $arr = array();
    while($result = mysql_fetch_assoc($res)){
      $arr[] = $result;
    }
    return $arr;
  }
}
$mysql = mysqldb::getInsance();