This is a little late... but I'm old and slow.......
Regarding Extending PDOStatement and PDO I found that sending the PDOExtended class by reference helps:
    In the constructor after parent::__construct() :
$this->setAttribute(\PDO::ATTR_STATEMENT_CLASS,array('PDOStatementExtended', [&$this]));}

And in 
class PDOStatementExtended extends \PDOStatement
{
  
  protected function __construct
  (
    \PDO &$PDO,
   )