[rules-users] Error in MVEL execution (optimization?)

[Mario Fusco]

Hi, 

I was investigating this issue and just found the cause of the double
evaluation of the pattern. The problem is in the
EqualityEvaluatorsDefinition.BooleanEqualEvaluator.evaluate() method:

https://github.com/droolsjbpm/drools/blob/master/drools-core/src/main/java/org/drools/base/evaluators/EqualityEvaluatorsDefinition.java#L552

As you can see here the extractor is invoked twice: first with isNullValue()
and then with getBooleanValue() and both these invocations cause in turn the
evaluation of the pattern. 

Unfortunately this is necessary to avoid a NullPointerException when
unboxing the primitive type. The (ugly) alternative would be to just invoke
the getBooleanValue() method in a try/catch block and act accordingly when a
NPE is thrown.

The good news is that I just finished to develop a totally new (and faster)
implementation of constraints evaluation. I already checked that this new
implementation doesn't suffer of this issue and it will be available in
Drools 5.4.

Mario

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