My gut instinct would say that this is possibly correct.

I’ve not looked at the mvel code but if all your types are strings then it makes sense for it to pick the most type specific operator first. Multiplication only works on numbers so it attempts to convert them but the + operator is defined on strings and therefore is a closer match for strings as you are assigning the result to a string.

I haven’t tried it but you could liberally sprinkling in brackets and type casts to get what you want, eg:

t.out = (double)(t.in2*t.in3) + (double)(t.in3*t.in4) + (double)(t.in2*t.in4);

Thomas

From: rules-users-bounces@lists.jboss.org [mailto:rules-users-bounces@lists.jboss.org] On Behalf Of Kinshuk Adhikary
Sent: 21 December 2009 02:48
To: rules-users@lists.jboss.org
Subject: [rules-users] Re-sending : Unexpected MVEL plus operator behavior(string-to-double), in consequence block

Using
drools 5.1
mvel 2-2.0.14

In consequence (then) block : (dialect strict or not does not make a difference)

Trying to sum up some numbers after a multiplication operation. For example :

t.out = t.in2*t.in3 + t.in3*t.in4 + t.in2*t.in4;

(the object t has all its attributes of the type String), all the t.in parameters are actually numbers-as-strings.

So the multiplication is going on fine, as expected, but the addition (+) sign, is concatenating instead of adding.

So the for inputs "1", "2" and "3", the result looks something like : 2.06.03.0 (i.e concetenated) instead of the expected 11.0.

What is going worng How does the + operator decide to do concat instead of doing addition.

Any documentation on this + operator logic ?

Note : The above works fine when I use MVEL without Drools.

Thanks