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From Andres Almiray <>
Subject Re: suggestion: ImplicitSafeNavigation annotation
Date Tue, 14 Aug 2018 12:31:31 GMT
This is a good example of a feature that can be experimented with as an
external AST transformation, there's no need to add it to core just yet.

Advantages of such approach:
 - faster development/release cycle.
 - can target specific Groovy version to begin with.
 - may break compatibility until feature works as expected.

Adding this feature to core in an early stage (conception) is too early

Remember that @TailCall started life as an external AST xform, it was added
to core when it became mature enough :-)


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On Tue, Aug 14, 2018 at 1:28 PM, ocs@ocs <> wrote:

> Gentlemen,
> some NPE-related problems of today brought me to re-interate one of my
> older suggestions.
> We have the so-called “safe navigation”[*], which in some cases allows a
> null to be propagated out of an expression instead of throwing a NPE. At
> the moment, it can be triggered for a particular sub-expression (like
> property/method-call and, as of 3, newly also indexing) using a question
> mark (e.g., “foo?.bar()” or “foo?[bar]”).
> Do please correct me if I am wrong, but far as I know, there still are
> expressions which do not allow the “safe mode”, e.g., arithmetic (“a+b”
> etc). Furthermore, there are cases when one simply wants a bigger block of
> code to contain only null-propagating expressions and never NPE; in such
> case, using the question mark syntax is both inconvenient and error-prone
> (for it is very easy to forget one of the lot of question marks needed in
> such a code, and then get an uncaught unwanted NPE).
> For these reasons, I would suggest adding a new annotation, whose name
> might be e.g., “ImplicitSafeNavigation”; it would simply force a
> null-propagation to be implicitly and automatically used for *all*
> expressions in the annotated scope, i.e., NPE would never be thrown for
> them; for example:
> ===
> @ImplicitSafeNavigation class Foo {
>  static foo(a,b,c,d,e) {
>*c[d]<<e.bax() // just e.g.; would work with *any* expression
> which NPEs today
>  }
> }
> assert null ==,null,null,null,null)
> ===
> I wonder whether this enhancement would be possible to implement in some
> forthcoming Groovy release? Myself, I believe it would help tremendously.
> If feasible, then it is for a further discussion whether in the scope of
> this annotation
> (a) a safe-navigation syntax (“foo?.bar”) should be ignored as superfluous;
> (b) or, whether in this scope it should reverse the behaviour to trigger
> an NPE anyway;
> (c) or, whether it should be ignored as (a), and aside of that it would be
> worth the effort (and technically possible) to add another syntax to force
> NPE over a particular sub-expression (e.g., “foo!.bar”).
> Thanks and all the best,
> OC
> [*] The name might not be quite apt, for propagating a null is not
> inherently safer than NPEing; those are simply two different approaches,
> both of which serve best in different circumstances. A better name would be
> something like “null-propagating” or “non-NPE” mode, I guess. Myself, I
> don't think we should change the name though, for all are used to it.

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