if we do implicit .? support people will still be able to do null
checks. So it's not one or the other.
Mark
On 28/07/2011 20:07, Greg Barton wrote:
+1
Naw....
+billion
--- On *Thu, 7/28/11, Edson Tirelli /<ed.tire...@gmail.com>/* wrote:
From: Edson Tirelli <ed.tire...@gmail.com>
Subject: Re: [rules-users] Condition syntax to access Map
To: "Rules Users List" <rules-users@lists.jboss.org>
Date: Thursday, July 28, 2011, 1:13 PM
All,
I think we need to differentiate paradigms here. When using
rules, contrary to imperative code, what we are doing is pattern
matching.
X( a.b.c == <value> )
In the above case, we are looking for Xs that make that whole
constraint true (i.e. match). If a or b are null, the whole
expression will be false, does not matter the value of c or the
value it is being compared against. Raising a null pointer
exception, IMO, brings no advantage at all to the table... on the
contrary, makes writing rules more difficult.
Another example we had in the past:
class Circle implements Shape
class Square implements Shape
rule X
when
Circle() from $shapes
...
In the above example, $shapes is a list and the rule is clearly
looking for Circles. If there are Squares in there, they will just
not match. Raising a ClassCastException like it would happen in an
imperative language brings no advantage to the table, IMO.
So, IMO, all property navigation should be null pointer safe in
the LHS of the rules.
This is not what happens today, but I think it should be fixed.
Edson
2011/7/28 Vincent LEGENDRE <vincent.legen...@eurodecision.com
</mc/compose?to=vincent.legen...@eurodecision.com>>
Hi all,
I agree with W. : NPE should be the default, and "null" cases
behaviour should be planned by programmers.
But I am not sure about using a new operator in rules (and do
the update in Guvnor ...).
Why not using some drools annotations on the getter specifying
the behaviour of an eval on a null value returned by this
getter ?
And may be these annotation could be added to an existing POJO
via the declared type syntax (just like event role in fusion) ?
Vincent.
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Edson Tirelli
JBoss Drools Core Development
JBoss by Red Hat @ www.jboss.com <http://www.jboss.com>
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