PHP延迟静态绑定

/*基类*/  
class BaseModel  
{  
  
    private static $instance = null;  
  
    public static function instance()  
    {  
  
        if (empty(self::$instance)) {  
  
            self::$instance = new self();  
        }  
  
        return self::$instance;  
    }  
}

/*商品类*/  
class GoodModel extends BaseModel{  
  
    public function getInfoById($goodId){  
  
        return array(  
            'id'=>$goodId,  
            'name'=>'小苹果',  
            'logo'=>'http://t3.qlogo.cn/mbloghead/65518bb9e5287fcd5864/180'  
        );  
    }  
}  
  
################################################################  
$good = GoodModel::instance();  
  
var_dump($good);

object(BaseModel)#1 (0) {  
}

class BaseModel  
{  
  
    private static $instance = null;  
  
    public static function instance()  
    {  
  
        if (empty(self::$instance)) {  
  
            self::$instance = new static();  
        }  
  
        return self::$instance;  
    }  
}

object(GoodModel)#1 (0) {  
}

class BaseModel  
{  
  
    private static $instance = null;  
  
    public static function instance()  
    {  
  
        if (empty(self::$instance)) {  
  
            $className = get_called_class();  
            self::$instance = new $className();  
        }  
  
        return self::$instance;  
    }  
}