protected function getEvaluatorByOperatorType($operator)
    {
        $evaluatorsByOperator = array();
        $evaluatorsByOperator[self::AND_OPERATOR] = 'andEvaluator';
        $evaluatorsByOperator[self::OR_OPERATOR] = 'orEvaluator';
        $evaluatorsByOperator[self::NOT_OPERATOR] = 'notEvaluator';

        return $evaluatorsByOperator[$operator];
    }