[rules-users] Benefits of pluggable operators

[Wolfgang Laun]

I'm inclined to think that a well-implemented operator can provide a
little bit more "cushioning" for the rule author. In the given
example, key.startsWith("abc") would throw an NPE if key is null. The
operator silently handle this case and simply return false.

Another thing is that operators can be used with the "single left hand
side" expression pattern, i.e.,
   field opa x || opb y || opc y
Syntactic sugar, certainly, but occasionally quite convenient.

-W


On 24/05/2013, Edson Tirelli <ed.tirelli at gmail.com> wrote:
>    Thomas,
>
>    Pluggable operators were developed much before we supported free form
> expressions, but nowadays they can be used for the same purpose. It is then
> a matter of preference basically. You can still develop and use pluggable
> operators if that makes your rule more readable by hiding complexity
> related to parameter passing or something that would be required in a
> method call, but I can't think of any advantage or disadvantage in either
> approach in terms of performance or cost.
>
>    If I remember correctly, pluggable operators were developed for Drools
> 4.0, while free form expressions were only fully functional in 5.3+
> (limited functionality in 5.2).
>
>    Edson
>
>
> On Fri, May 24, 2013 at 10:54 AM, Thomas Grayson
> <tgrayson at bluemetal.com>wrote:
>
>>  What are the benefits of using pluggable operators (implementations of
>> org.drools.base.evaluators.EvaluatorDefinition such str, matches, or
>> before) versus simply making an equivalent function call?  I’ve read the
>> Creating
>> pluggable
>> operators<http://blog.athico.com/2010/06/creating-pluggable-oprators.html>blog
>> post.  Apart from saying that the Eclipse plugin can recognize these
>> operators, it doesn’t really make a case for why I’d want to create my
>> own
>> implementation.  One might argue that operators enhance reusability, but
>> a
>> static method offers much the same benefit.  Does a pluggable operator
>> have
>> any optimization, caching, or other advantage?****
>>
>> ** **
>>
>> For example, here are two ways to match the start of a string in a
>> property of a fact, one using  the “str[startsWith]” operator and another
>> with Java’s String.startsWith method:****
>>
>> ** **
>>
>> *declare* Fact****
>>
>>     key : String @key****
>>
>> *end*****
>>
>> ** **
>>
>> *rule* "Use operator"****
>>
>>     *when*****
>>
>>         Fact(key str[startsWith] "abc")****
>>
>>     *then*****
>>
>>         // do something****
>>
>> *end*****
>>
>> ** **
>>
>> *rule* "Use method"****
>>
>>     *when*****
>>
>>         Fact(key.startsWith("abc"))****
>>
>>     *then*****
>>
>>         // do something****
>>
>> *end*****
>>
>> ** **
>>
>> Does one of these perform better than the other?****
>>
>> ** **
>>
>> Best wishes,****
>>
>> Tom****
>>
>> ** **
>>
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>>
>
>
>
> --
>   Edson Tirelli
>   JBoss Drools Core Development
>   JBoss by Red Hat @ www.jboss.com
>