[rules-users] Adding a custom operator to drools?

[Michael Zimmermann]

Hi Edson,

I think I got it working :-)

Edson Tirelli wrote:
> For an example, look at the file SetEvaluatorsDefinition and look at
> the BaseMemberOf inner class. So, all the logic is in there, but we
> still used subclasses just to set the constructor attributes and
> override the toString() method, but you could still implement
> everything in a single class I guess. 

Yes, this approach makes sense as long as you don't need to use the
different VariableContextEntry subclasses for handling double, char etc.
Yet, this can be handled, too.

toString():
You can avoid subclassing from your BaseMyEvaluatorClass to override
toString() by using a string method like:

public String toString() {
  return getValueType().getName() + " " +
         getOperator().getOperatorString();
}

Regarding the evaluator API:
If you only need one evaluator class (subclassed from BaseEvaluator),
personally I don't like the > 10 static calls to
    addEvaluator(type, operator, myEvaluatorInstance)
in the EvaluatorDefinition class.

So, how about adding the method addDefaultEvaluator(operator,
evaluatorClass) to EvaluatorCache, see attachment?
This would allow you to register a evaluator as default and only overide
the special cases...


PS: If you are interested I will write some small tutorial about custom
evaluators / operators in drools trunk. This might take a week or two,
though. Any preferences regarding the format?

Thanks for the help....

cu, Michael

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