# Problem with getArgDocString

**URL:** <https://forum.inductiveautomation.com/t/problem-with-getargdocstring/14852>\
**Category:** Module Development\
**Created:** [July 21, 2017, 10:59am UTC](https://forum.inductiveautomation.com/t/problem-with-getargdocstring/14852 "2017-07-21T10:59:24Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![alain.pfeiffer](https://avatars.discourse-cdn.com/v4/letter/a/fbc32d/32.png) [@alain.pfeiffer](https://forum.inductiveautomation.com/u/alain.pfeiffer)\
**Post date:** [July 21, 2017, 10:59am UTC](https://forum.inductiveautomation.com/t/problem-with-getargdocstring/14852/1 "2017-07-21T10:59:24Z")

</div>

Hello everyone,

I got a code from Travis Cox where he showed me how I can add an Expression function. The name of the example class is "ConvertBase". I used that as a template and coded the functions I was asked to implement. However, for whatever reason, The getArgDocString can be seen in inductive automation with Travis' example but not with the functions I implemented. Does anyone know why?

public class ConvertBase implements Function:

> ```
> @Override
> public QualifiedValue execute(Expression[] expressions) throws ExpressionException {
> QualifiedValue from = expressions[0].execute();
> QualifiedValue to = expressions[1].execute();
> QualifiedValue numberToConvert = expressions[2].execute();
> 
> ```

> ```
> Quality quality = DataQuality.worstOf(from.getQuality(), to.getQuality());
> quality = DataQuality.worstOf(quality, numberToConvert.getQuality());
> 
> ```

> ```
> Integer inputInt = Integer.valueOf(numberToConvert.getValue().toString(), (Integer) from.getValue());
> String output = Integer.toString(inputInt, (Integer) to.getValue());
> 
> ```

> ```
> return new BasicQualifiedValue(output, quality);
> }
> 
> ```

> ```
> @Override
> public void initArgs(Expression[] args) {
> if (!validateNumArgs(args.length)) {
> throw new RuntimeException("Function '" + "ConvertBase" + "(" + getArgDocString()
> + ")' does not work with " + args.length + " arguments.");
> } else {
> for (int i = 0; i < args.length; i++) {
> if (!validateArgType(i, args[i].getType())) {
> throw new RuntimeException("Type mismatch: Argument " + i + " for function '" + "ConvertBase"
> + "(" + getArgDocString() + ")' is an invalid type.");
> }
> }
> }
> }
> 
> ```

> ```
> protected boolean validateNumArgs(int num) {
> return num == 3;
> }
> 
> ```

> ```
> protected boolean validateArgType(int argNum, Class<?> type) {
> boolean ret = false;
> 
> ```

> ```
> switch (argNum) {
> case 0:
> ret = type == Integer.class;
> break;
> case 1:
> ret = type == Integer.class;
> break;
> case 2:
> ret = type == String.class;
> break;
> }
> 
> ```

> ```
> return ret;
> }
> 
> ```

> ```
> @Override
> public String getArgDocString() {
> return "from, to, numberToConvert";
> }
> 
> ```
> 
> }

public class TagValue implements Function :

> @Override  
> public QualifiedValue execute(Expression args) throws ExpressionException {  
> //Initialization phase  
> String database = args[0].execute().getValue().toString();  
> String tagName = args[1].execute().getValue().toString();  
> if(args.length == 3){  
> this.defaultErrorValue = Double.parseDouble(args[2].execute().getValue().toString());  
> }
> 
> ```
> PWPreparedStatement preparedStatement = new PWPreparedStatement(server, database, tagName);
> return new BasicQualifiedValue(preparedStatement.getResult(defaultErrorValue));
> 
> ```
> 
> }

> @Override  
> public String getArgDocString() {  
> return "db, tagname, defaultError(optional)";  
> }
> 
> protected boolean validateNumArgs(int num) {  
> if (num == 2 || num == 3){  
> return true;  
> }  
> return false;  
> }

> ```
> protected boolean validateArgType(int argNum, Class<?> type) {
> boolean ret = false;
>     
> switch (argNum) {
> case 0:
> ret = type == String.class;
> break;
> case 1:
> ret = type == String.class;
> break;
> case 2:
> ret = type == Double.class;
> break;
> }
> 
> ```

> ```
> return ret;
> }
> 
> ```

> @Override  
> public void initArgs(Expression args) {  
> if (!validateNumArgs(args.length)) {  
> throw new RuntimeException("Function '" + "TagValue" + "(" + getArgDocString()  
> + ")' does not work with " + args.length + " arguments.");  
> } else {  
> for (int i = 0; i \< args.length; i++) {  
> if (!validateArgType(i, args[i].getType())) {  
> throw new RuntimeException("Type mismatch: Argument " + i + " for function '" + "TagValue"  
> + "(" + getArgDocString() + ")' is an invalid type.");  
> }  
> }  
> }  
> }  
> }

Here the picture.

 ![](https://us1.discourse-cdn.com/inductiveautomation/original/2X/b/bb19567744e98c4ec62f7ba241f689887c212757.png)

Thank you