public static String arg0Type(ExprNodeGenericFuncDesc expr) {
    return expr.getChildren().get(0).getTypeString();
  }
The GenericUDFs might need their children output to be cast to the given castType.
This method returns a cast expression that would achieve the required casting.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/VectorizationContext.java