[rules-users] Condition syntax to access Map

[Mark Proctor]

On 28/07/2011 13:53, Wolfgang Laun wrote:
> Two points to consider:
>
> (1) If a programmer writes
>    a.getB().getC() == <something>
> and a NPE happens due to a.getB() == null we may distinguish (a) and 
> (b) - see below.
>
> (a) The setup is so that this is to be expected but the programmer 
> forgot to take this possibility into account. Then we have:
>
> (a1) The consequence of a.getB() == null should be the same as 
> a.getB().getC() == null.
>
> (a2) If a.getB() == null, something else needs to be done, e.g., 
> a.setB(x). If this is silently covered by the system, the absence of 
> handling will not be detected so easily.
>
> (b) The assumption is that a.getB() should never be == null in the 
> first place, but some other error (in data or code) caused this. If 
> this is silently covered by the system, this error will not be 
> detected so easily.
>
>
> (2) If a.getB().getC() == <something> returns false if a.getB() is 
> null, is this also the desired result if <something> is "null", i.e., 
> do you want
>    a.getB().getC() == null
> to be false if a.getB() == null ?
>
> "Null safe navigation" is a nice try and *may* be tolerable, but it 
> should never be the default.
ok, sounds like we just need to add .? support into our parser then - if 
it's not already supported.

Mark
>
> -W
>
>
> On 28 July 2011 14:06, bolsover <david at bolsover.com 
> <mailto:david at bolsover.com>> wrote:
>
>     Thanks for the pointer to the MVEL documents - I can forsee null-safe
>     operator user.?manager.name <http://manager.name> syntax being
>     most useful.
>
>     As for making the null test the default action - I'm not sure - I
>     can't say
>     I have ever actually 'wanted' a nullpointer - but there may be
>     some special
>     case.
>
>     David
>
>     --
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