Description:
------------
---
From manual page: http://www.php.net/internals2.objects
---
class MyPDO  extends PDO
{
    private static $instance = null;
    function  __construct(){
        try{
        parent::__construct("mysql:host=localhost;port=3306;dbname=blog", "root", "");
        parent::setAttribute( PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION );
        }catch(PDOException $e){
            echo 'Exception in constructor'.print_r($e->trace(),true);
        }

    }

   static public function getDB(){
        if(self::$instance == null){
            self:$instance = new MyPDO();
        }
        return self::$instance;
    }

    function selectAll($sql){
            $stmt = self::$instance->prepare($sql);
            $stmt->execute(array(":cat_id"=>1));
            return $stmt->fetchAll(PDO::FETCH_ASSOC);
    }

}

Expected result:
----------------
class MyPDO  extends PDO
{
    private static $instance = null;
    function  __construct(){
        try{
        parent::__construct("mysql:host=localhost;port=3306;dbname=blog", "root", "");
        parent::setAttribute( PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION );
        }catch(PDOException $e){
            echo 'Exception in constructor'.print_r($e->trace(),true);
        }

    }

   static public function getDB(){
        if(self::$instance == null){
            self::$instance = new MyPDO();** ERROR SHOULD BE REPORTED HERE
WHEN USING self:$instance , it SHOULD BE THE SCOPE RESOLUTION OPERATOR WITH DOUBLE COLON ::...Sorry if it is not a bug but some thing i don't have knowledge of..
        }
        return self::$instance;
    }

    function selectAll($sql){
            $stmt = self::$instance->prepare($sql);
            $stmt->execute(array(":cat_id"=>1));
            return $stmt->fetchAll(PDO::FETCH_ASSOC);
    }

}