public function all($strategy = null)
    {
        if ($this instanceof \Iterator) {
            $strategy = conversions\mixed_to_value_getter($strategy);

            foreach ($this as $item) {
                $tempVarPhp54 = call_user_func($strategy, $item);
                if (empty($tempVarPhp54)) {
                    return false;
                }
            }

            return true;
        }

        return null;
    }