Hi Maurizio, > > I second what Mandy says. > > First let me start by saying that this enhancement will be a great > addition to our platform; back in the days when I was teaching some Java > classes at the university, I was very aware of how hard it is to > diagnose a NPE for someone novel to Java programming. A trained eye of > course can quickly scan the line where an exception occurs, and quickly > isolate the couple of problematic spots which could have caused an > exception. But it takes time to get to that point, and having some > helpful messages to help you to get to that point is, IMHO a valuable > goal in itself. Thanks!
> I also think that the design space for such an enhancement is non > trivial, and would best be explored (and captured!) in a medium that is > something other than a patch. What kind of improvements should we add to > the NPE exception? What happens if the NPE already has an user-provided > details message? Should the enhancement make use of optional debugging > classfile attributes (you touch this in your nice RFE). And again, what > are the performance considerations we deem important for this work to be > declared successful? And, maintenance-wise, what is the right way to > implement the enhancement? Should we implement that as a pure VM > feature, should we implement it on top of the existing VM, using some > classfile manipulation (**) ? Or a combination of those? I'm working on a text... > As you can see, there are so many question this enhancement raises that > I think going straight for a code review can be a premature move; people > will be coming at the review table with different answers to the above > set of questions (and maybe additional questions too :-)), and that > could make the review process hard and frustrating for all the parties > involved. So I warmly suggest we take a step back from the code, and > formulate a proposal for enhancing NPE messages in Java; in this sense, > a JEP seems to me the most natural way to move forward. Well, I had the code around, so I started this enhancement just showing our code. I guess a prototype is always a good starting point. > (**) I have a quick and dirty prototype of that built using ASM which > I'm happy to share, in case you are interested taking a look when > evaluating alternatives. Yes, it would be nice if you shared that. Best regards, Goetz. > > Cheers > Maurizio > > > On 14/03/2019 00:42, Mandy Chung wrote: > > Hi Goetz, > > > > Roger, Coleen, Maurizio and I talked about this proposed feature. > > We all think that improving NPE message is a useful enhancement for > > the platform and helps developers to tell what causes NPE. > > > > This is not a small enhancement. Diving into a large code review > > would not be the best way to move this forward as you can see the > > discussion so far. > > > > It would help if you can start with writing down the problem and > > the proposal like what improvements are proposed and under what > > circumstances may be acceptable that NPE message won't be improved. > > This would get the discussion on the proposal feature and then > > the discussion of the best way to to implement it in the VM, library, > > or combination. You can consider using the JEP template that gives > > you a good structure to follow for the write up. > > > > What do you think? > > > > Mandy
