That's not how I meant my sample eval helper method to be used :-) (for brevity I will write neval for eval(true) here)
What I meant was: How easy would it be to get a similar result to what you want, by wrapping a few key places (e.g. a whole method body) in your code in neval { ... } ? Evidently that would just mean that any NPE inside the e.g. method would lead to the whole method result being null. To give a simple example: final x = a?.b?.c?.d could be written as final x = neval { a.b.c.d } Of course the two expressions are not semantically identical, since neval will transform any NPE inside evaluation of a, b, c, and d into the result null - but since you say you never want to see any NPEs... (The performance of neval should be ok, since I do not assume that you expect your code to actually encounter null values, and accordingly NPEs, all the time) -------- Ursprüngliche Nachricht --------Von: "ocs@ocs" <o...@ocs.cz> Datum: 14.08.18 23:14 (GMT+00:00) An: dev@groovy.apache.org Betreff: Re: suggestion: ImplicitSafeNavigation annotation mg, On 14 Aug 2018, at 11:36 PM, mg <mg...@arscreat.com> wrote: I am wondering: In what case does what you are using/suggesting differ significantly from simply catching a NPE that a specific code block throws and letting said block evaluate to null in that case: def eval(bool nullSafeQ, Closure cls) { try { return cls() } catch(NullPointerException e) { if(nullSafeQ) { return null } throw e }} Conceptually, not in the slightest. In practice, there's a world of difference. For one, it would be terrible far as the code cleanness, fragility and readability are concerned — even worse than those ubiquitous question marks: === the code should look, say, like this ===@ImplicitSafeNavigation def foo(bar) { def x=baz(bar.foo)?:bax(bar.foo) x.allResults { def y=baz(it) if (y>1) y+bax(y-1) else y–bax(0) }}=== the eval-based equivalent would probably look somewhat like this ===def foo(bar) { def x=eval(true){baz(eval(true){bar.foo})?:bax(bar.foo)} eval(true){ x.allResults { def y=eval(true){baz(it)} if (y>1) eval(true){y+bax(y-1)} else eval(true){y–bax(0)} } }}=== and quite frankly I am not even sure whether the usage of eval above is right and whether I did not forget to use it somewhere where it should have been. It would be ways easier with those question marks. Also, with the eval block, there might be a bit of a problem with the type information: I regret to say I do not know whether we can in Groovy declare a method with a block argument in such a way that the return type of the function is automatically recognised by the compiler as the same type as the block return value? (Definitely I don't know how to do that myself; Cédric or Jochen might, though ;)) Aside of that, I wonder about the efficiency; although premature optimisation definitely is a bitch, still an exception harness is not cheap if an exception is caught, I understand. (It feels a bit like what you wants is tri-logic/SQL type NULL support in Groovy, not treating Java/Groovy null differently...) In fact what I want is a bit like the Objective-C simple but very efficient and extremely practical nil behaviour, to which I am used to and which suits me immensely. Agreed, the Java world takes a different approach (without even the safe navigation where it originated!); I have tried to embrace that approach a couple of times, and always I have found it seriously lacking. I do not argue that the null-propagating behaviour is always better; on the other hand, I do argue that sometimes and for some people it definitely is better, and that Groovy should support those times and people just as well as it supports the NPE-based approach of Java. Thanks and all the best,OC -------- Ursprüngliche Nachricht --------Von: "ocs@ocs" <o...@ocs.cz> Datum: 14.08.18 17:46 (GMT+00:00) An: dev@groovy.apache.org Betreff: Re: suggestion: ImplicitSafeNavigation annotation Jochen, On 14 Aug 2018, at 6:25 PM, Jochen Theodorou <blackd...@gmx.org> wrote:Am 14.08.2018 um 15:23 schrieb ocs@ocs: H2, However, “a+b” should work as one would expect Absolutely. Me, I very definitely expect that if a happens to be null, the result is null too. (With b null it depends on the details of a.plus implementation.) the counter example is null plus String though Not for me. In my world, if I am adding a string to a non-existent object, I very much do expect the result is still a non-existent object. Precisely the same as if I has been trying to turn it to lowercase or to count its character or anything. Whilst I definitely do not suggest forcing this POV to others, to me, it seems perfectly reasonable and 100 per cent intuitive. Besides, it actually (and expectably) does work so, if I use the method-syntax to be able to use safe navigation: ===254 /tmp> <q.groovy String s=nullprintln "Should be null: ${s?.plus('foo')}"255 /tmp> /usr/local/groovy-2.4.15/bin/groovy qWARNING: An illegal reflective access operation has occurred... ...Should be null: null256 /tmp> === which is perfectly right. Similarly, a hypothetical “null?+'foo'” or “@ImplicitSafeNavigation ... null+foo” should return null as well, to keep consistent. (Incidentally, do you — or anyone else — happen to know how to get rid of those pesky warnings?) Thanks and all the best,OC