<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:x="urn:schemas-microsoft-com:office:excel" xmlns:p="urn:schemas-microsoft-com:office:powerpoint" xmlns:a="urn:schemas-microsoft-com:office:access" xmlns:dt="uuid:C2F41010-65B3-11d1-A29F-00AA00C14882" xmlns:s="uuid:BDC6E3F0-6DA3-11d1-A2A3-00AA00C14882" xmlns:rs="urn:schemas-microsoft-com:rowset" xmlns:z="#RowsetSchema" xmlns:b="urn:schemas-microsoft-com:office:publisher" xmlns:ss="urn:schemas-microsoft-com:office:spreadsheet" xmlns:c="urn:schemas-microsoft-com:office:component:spreadsheet" xmlns:odc="urn:schemas-microsoft-com:office:odc" xmlns:oa="urn:schemas-microsoft-com:office:activation" xmlns:html="http://www.w3.org/TR/REC-html40" xmlns:q="http://schemas.xmlsoap.org/soap/envelope/" xmlns:rtc="http://microsoft.com/officenet/conferencing" xmlns:D="DAV:" xmlns:Repl="http://schemas.microsoft.com/repl/" xmlns:mt="http://schemas.microsoft.com/sharepoint/soap/meetings/" xmlns:x2="http://schemas.microsoft.com/office/excel/2003/xml" xmlns:ppda="http://www.passport.com/NameSpace.xsd" xmlns:ois="http://schemas.microsoft.com/sharepoint/soap/ois/" xmlns:dir="http://schemas.microsoft.com/sharepoint/soap/directory/" xmlns:ds="http://www.w3.org/2000/09/xmldsig#" xmlns:dsp="http://schemas.microsoft.com/sharepoint/dsp" xmlns:udc="http://schemas.microsoft.com/data/udc" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:sub="http://schemas.microsoft.com/sharepoint/soap/2002/1/alerts/" xmlns:ec="http://www.w3.org/2001/04/xmlenc#" xmlns:sp="http://schemas.microsoft.com/sharepoint/" xmlns:sps="http://schemas.microsoft.com/sharepoint/soap/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:udcs="http://schemas.microsoft.com/data/udc/soap" xmlns:udcxf="http://schemas.microsoft.com/data/udc/xmlfile" xmlns:udcp2p="http://schemas.microsoft.com/data/udc/parttopart" xmlns:wf="http://schemas.microsoft.com/sharepoint/soap/workflow/" xmlns:dsss="http://schemas.microsoft.com/office/2006/digsig-setup" xmlns:dssi="http://schemas.microsoft.com/office/2006/digsig" xmlns:mdssi="http://schemas.openxmlformats.org/package/2006/digital-signature" xmlns:mver="http://schemas.openxmlformats.org/markup-compatibility/2006" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns:mrels="http://schemas.openxmlformats.org/package/2006/relationships" xmlns:spwp="http://microsoft.com/sharepoint/webpartpages" xmlns:ex12t="http://schemas.microsoft.com/exchange/services/2006/types" xmlns:ex12m="http://schemas.microsoft.com/exchange/services/2006/messages" xmlns:pptsl="http://schemas.microsoft.com/sharepoint/soap/SlideLibrary/" xmlns:spsl="http://microsoft.com/webservices/SharePointPortalServer/PublishedLinksService" xmlns:Z="urn:schemas-microsoft-com:" xmlns:st="" xmlns="http://www.w3.org/TR/REC-html40"><head><meta http-equiv=Content-Type content="text/html; charset=us-ascii"><meta name=Generator content="Microsoft Word 12 (filtered medium)"><style><!--
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</o:shapelayout></xml><![endif]--></head><body bgcolor=white lang=EN-US link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>I’m 100% with Edson on this one. <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Requiring explicit syntax, whether via null checks or .?, can have a big impact on the clarity and level of declarativeness (word?) of a given ruleset. It also makes it a great deal harder to develop DSLs and systems to put rules into the hands of non-developers because then you’re requiring those users to bring with them the imperative programming mindset of checking every data point before using it. <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>I think that Edson’s example of making the whole expression false if any object on the call stack is null independent of the value is an excellent convention.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Joe<o:p></o:p></span></p><div><div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'><p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext'>From:</span></b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext'> rules-users-bounces@lists.jboss.org [mailto:rules-users-bounces@lists.jboss.org] <b>On Behalf Of </b>Mark Proctor<br><b>Sent:</b> Thursday, July 28, 2011 1:35 PM<br><b>To:</b> rules-users@lists.jboss.org<br><b>Subject:</b> Re: [rules-users] Condition syntax to access Map<o:p></o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>if we do implicit .? support people will still be able to do null checks. So it's not one or the other.<br><br>Mark<br>On 28/07/2011 20:07, Greg Barton wrote: <o:p></o:p></p><table class=MsoNormalTable border=0 cellspacing=0 cellpadding=0><tr><td valign=top style='padding:0in 0in 0in 0in'><p class=MsoNormal>+1 <o:p></o:p></p><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>Naw....<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>+billion<br><br>--- On <b>Thu, 7/28/11, Edson Tirelli <i><a href="mailto:ed.tirelli@gmail.com"><ed.tirelli@gmail.com></a></i></b> wrote:<br><br><o:p></o:p></p><p class=MsoNormal style='margin-bottom:12.0pt'><br>From: Edson Tirelli <a href="mailto:ed.tirelli@gmail.com"><ed.tirelli@gmail.com></a><br>Subject: Re: [rules-users] Condition syntax to access Map<br>To: "Rules Users List" <a href="mailto:rules-users@lists.jboss.org"><rules-users@lists.jboss.org></a><br>Date: Thursday, July 28, 2011, 1:13 PM<o:p></o:p></p><div id=yiv864855709><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal> All,<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal> I think we need to differentiate paradigms here. When using rules, contrary to imperative code, what we are doing is pattern matching.<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>X( a.b.c == <value> )<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal> 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. <o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal> Another example we had in the past:<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>class Circle implements Shape<o:p></o:p></p></div><div><p class=MsoNormal>class Square implements Shape<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>rule X<o:p></o:p></p></div><div><p class=MsoNormal>when<o:p></o:p></p></div><div><p class=MsoNormal> Circle() from $shapes<o:p></o:p></p></div><div><p class=MsoNormal>...<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal> 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.<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal> So, IMO, all property navigation should be null pointer safe in the LHS of the rules. <o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal> This is not what happens today, but I think it should be fixed.<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal> Edson<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal> <o:p></o:p></p></div><p class=MsoNormal style='margin-bottom:12.0pt'> <o:p></o:p></p><div><p class=MsoNormal>2011/7/28 Vincent LEGENDRE <<a href="/mc/compose?to=vincent.legendre@eurodecision.com" target="_blank">vincent.legendre@eurodecision.com</a>><o:p></o:p></p><div><div><p class=MsoNormal>Hi all,<br><br>I agree with W. : NPE should be the default, and "null" cases behaviour should be planned by programmers.<br>But I am not sure about using a new operator in rules (and do the update in Guvnor ...). <br>Why not using some drools annotations on the getter specifying the behaviour of an eval on a null value returned by this getter ? <br>And may be these annotation could be added to an existing POJO via the declared type syntax (just like event role in fusion) ?<br><span style='color:#888888'><br>Vincent.</span><o:p></o:p></p></div></div><p class=MsoNormal style='margin-bottom:12.0pt'><br>_______________________________________________<br>rules-users mailing list<br><a href="/mc/compose?to=rules-users@lists.jboss.org" target="_blank">rules-users@lists.jboss.org</a><br><a href="https://lists.jboss.org/mailman/listinfo/rules-users" target="_blank">https://lists.jboss.org/mailman/listinfo/rules-users</a><o:p></o:p></p></div><p class=MsoNormal><br><br clear=all><br>-- <br> Edson Tirelli<br> JBoss Drools Core Development<br> JBoss by Red Hat @ <a href="http://www.jboss.com" target="_blank">www.jboss.com</a><o:p></o:p></p></div><p class=MsoNormal style='margin-bottom:12.0pt'><br>-----Inline Attachment Follows-----<o:p></o:p></p><div><p class=MsoNormal>_______________________________________________<br>rules-users mailing list<br><a href="/mc/compose?to=rules-users@lists.jboss.org">rules-users@lists.jboss.org</a><br><a href="https://lists.jboss.org/mailman/listinfo/rules-users" target="_blank">https://lists.jboss.org/mailman/listinfo/rules-users</a><o:p></o:p></p></div></div></td></tr></table><p class=MsoNormal><br><br><br><o:p></o:p></p><pre>_______________________________________________<o:p></o:p></pre><pre>rules-users mailing list<o:p></o:p></pre><pre><a href="mailto:rules-users@lists.jboss.org">rules-users@lists.jboss.org</a><o:p></o:p></pre><pre><a href="https://lists.jboss.org/mailman/listinfo/rules-users">https://lists.jboss.org/mailman/listinfo/rules-users</a><o:p></o:p></pre><p class=MsoNormal><o:p> </o:p></p></div></body></html>