[rules-users] Unexpected behavior of accumulate() and insertLogical() when the result() goes from matching a constraint to not matching

[mikerod]

I agree that it is bad form to introduce unnecessary nulls.  I mostly did
that for the sake of simplicity in the example.  

I tried out your initial proposal of how to implement this, where you put
the logic previously in my `result` segment of the `accumulate` into the
"result pattern" segment of the rule instead.  This seems to have the effect
that I am going for, but I'm a little suprised that it produces different
results.

The reason I say this, is here:

$sample : SampleFact() from
						accumulate( $sf : SampleFact(), 
                        			init( SampleFact temp = null; ), 
                        			action( temp = ((null == temp) || ($sf.version >
temp.version)) ? $sf : temp; ), 
                        			result( ((null != temp) && (temp.value < 10)) ?
temp : null; ))	     

When a SampleFact is matched in the accumulate that has the highest version,
but does not have a value < 10, the `result` should
produce the value null, which I'd not expect to match the "result pattern"
of SampleFact().
So basically, I would have expected this to have the same effect as putting
the restricitons in the result pattern segment itself, as your example
showed me (i.e. SampleFact( value < 10 ) ).

Going with Davide's previous reply; 
the difference seems to be that if the `result` produces null, then it does
not match SampleFact(), and so *does not* override previous accumulate
activations that did match. 
However, when `result` produces a SampleFact that does not match SampleFact(
value < 10), it *does* override previous activations from the accumulate.

So I feel that there is a gap in my understanding of what is happening here
at this point.

I appreciate all the helpful feedback on this topic!



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