presto-main/src/main/java/io/prestosql/operator/unnest/UnnestOperator.java/UnnestOperator/createOperator
class UnnestOperator:        @Override
        public Operator createOperator(DriverContext driverContext)
        {
            checkState(!closed, "Factory is already closed");
            OperatorContext operatorContext = driverContext.addOperatorContext(operatorId, planNodeId, UnnestOperator.class.getSimpleName());
            return new UnnestOperator(operatorContext, replicateChannels, replicateTypes, unnestChannels, unnestTypes, withOrdinality, outer);
        }