presto-main/src/main/java/io/prestosql/operator/SetBuilderOperator.java/SetBuilderOperatorFactory/createOperator
class SetBuilderOperatorFactory:        @Override
        public Operator createOperator(DriverContext driverContext)
        {
            checkState(!closed, "Factory is already closed");
            OperatorContext operatorContext = driverContext.addOperatorContext(operatorId, planNodeId, SetBuilderOperator.class.getSimpleName());
            return new SetBuilderOperator(operatorContext, setProvider, setChannel, hashChannel, expectedPositions, joinCompiler);
        }