IIRC, there has been some discussion among Drools developers
to add this instanceof test automatically. But right now, the
instanceof is required - not necessarily in the posted way.

(1) Whether a Step object contains L as a subset
of its List<DescribedAddress> or in any other way should not be
exposed to the clients of this class. So, add a
   List<VendorAddress> getVendorAddresses()
to Step and hide the dirty details where they belong.

(2) With or without (1), in this particular situation, an accumulate
would be indicated which determines the VendorAddress with
maximum abcScore in one pass over all objects.

-W

On 26 August 2011 22:04, lhorton <LHorton@abclegal.com> wrote:
The following code works, but I think it's ugly.

the classes are:
DescribedAddress is a base class for addresses
VendorAddress extends DescribedAddress and implements method abcScore()
Step getLocations() is defined as a list of DescribedAddress objects but it
can also contain VendorAddress objects since they are a kind of
DescribedAddress

the LHS of the rule below extracts the VendorAddress with the highest
abcScore from step.locations

if I omit the eval(), i get ClassCastException on any DescribedAddress in
locations, since DescribedAddress cannot be cast to VendorAddress.

is there a more elegant / clean / efficient way to get only the
VendorAddress objects from locations?

rule "Find highest scored address"
dialect "mvel"
when
       $step : Step()
       $location : VendorAddress (eval($location instanceof VendorAddress ),
abcScore>9) from $step.getLocations()

       not $addr : VendorAddress (eval($addr instanceof VendorAddress
),abcScore > $location.abcScore) from $step.getLocations()

then
       System.out.println("high score is: " + $location.getAbcScore());
end

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