private VectorExpression getGenericUDFStructField(ExprNodeFieldDesc exprNodeFieldDesc,
      VectorExpressionDescriptor.Mode mode, TypeInfo returnType) throws HiveException {
    // set the arguments for GenericUDFStructField
    List<ExprNodeDesc> children = new ArrayList<>(2);
    children.add(exprNodeFieldDesc.getDesc());
    children.add(new ExprNodeConstantDesc(getStructFieldIndex(exprNodeFieldDesc)));

    return getVectorExpressionForUdf(null, GenericUDFStructField.class, children, mode, returnType);
  }
Returns a vector expression for a given expression
description.
@param exprDesc, Expression description
@param mode
@return {@link VectorExpression}
@throws HiveException
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/VectorizationContext.java