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From "ocs@ocs" <...@ocs.cz>
Subject Re: suggestion: ImplicitSafeNavigation annotation
Date Tue, 14 Aug 2018 12:37:37 GMT
Just a followup:

> On 14 Aug 2018, at 2:25 PM, ocs@ocs <ocs@ocs.cz> wrote:
> 
> what I would like to see in Groovy would be a way to intentionally switch to the non-NPE
null-propagating behaviour where needed by very explicit using of an appropriate annotation.

... considering that, instead of a simple annotation, one with a boolean parameter to switch
the behaviour on and off as needed might be better:

===
@ImplicitSafeNavigation(true) class Foo {
  static foo(a,b,c,d,e) {
    a.bar+b*c[d]<<e.bax() // just e.g.; would work with *any* expression which NPEs
today
  }
  @ImplicitSafeNavigation(false) bar(a) {
    a.bar
  }
}
assert null == Foo.foo(null,null,null,null,null)
Foo.bar(null) // throws NPE
===

> Begin forwarded message:
> 
> From: "ocs@ocs" <ocs@ocs.cz>
> Subject: suggestion: ImplicitSafeNavigation annotation
> Date: 14 August 2018 at 1:28:01 PM CEST
> To: dev@groovy.apache.org
> Reply-To: dev@groovy.apache.org
> 
> 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) {
>   a.bar+b*c[d]<<e.bax() // just e.g.; would work with *any* expression which NPEs
today
> }
> }
> assert null == Foo.foo(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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