public Builder setArgumentType(int index, String type) {
      argTypes[index] = ArgumentType.getType(type);
      return this;
    }
Builder builds a {@link Descriptor} object. Setter methods are provided to set the {@link Mode}, number
of arguments, argument types and expression types for each argument.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/VectorExpressionDescriptor.java