public function firstColumn()
    {
        static $first;

        if (!$first) {
            $columns = $this->columns();
            reset($columns);
            $first = key($columns);
            //\Zend\Debug\Debug::dump(get_class_methods($sheet)); die(__METHOD__);
        }
        return $first;
    }
public function firstColumn()
    {
        static $first;

        if (!$first) {
            $columns = $this->columns();
            reset($columns);
            $first = key($columns);
            //\Zend\Debug\Debug::dump(get_class_methods($sheet)); die(__METHOD__);
        }
        return $first;
    }
{@inheritDoc}