[External] : Re: JEP 405 update

[Gavin Bierman]

Thanks Remi. Yes, this text could be better (interestingly, it is unchanged from nearly a year ago!). I think you’d agree that *pattern matching* with nested patterns provides a null-safe approach to data access, right? That’s really what I am getting at. In that sense, record patterns are a key, because they support nesting of patterns. You are correct that the construct within which we surface pattern matching can have a say in the top-level treatment of null. Indeed, one of the things we are discussing at the moment is exactly whether switch should have a stronger opinion about top-level null! 

Let me see if I can work on the text some more. 

Thanks for the feedback,
Gavin

> On 9 Feb 2022, at 16:40, Remi Forax <forax at univ-mlv.fr> wrote:
> 
> Hi Gavin,
> I don't buy the argument that record patterns promote a null-safe style of programming as this is stated several times in the JEP.
> 
> The ""null-safety"" (notice the air quotes) mostly comes from the instanceof or the switch (which semantics is equivalent of a cascade of if instanceof), not from the record pattern by itself.
> 
> You can argue that when a record pattern is nested a nullcheck appears, but it's more than the underlying semantics is a degenerated instanceof when the declared type and the instanceof type are the same.
> 
> The record pattern is about destructuring after the instanceof/nullcheck has been done, so i find that argument counter productive because it does not help to understand the semantics.
> 
> Also, we have talked several times to introduce the record pattern when doing an assignment
>  Point point = ...
>  Point(int x, int y) = point;
>  // can use x and y here !
> 
> This will throw a NPE if point is null, similarly to an unboxing operation.
> 
> The null-safety is not attached to the record pattern per se but by the container that use it (instanceof, case of a switch, enclosing pattern).
> 
> regards,
> Rémi
> 
> ----- Original Message -----
>> From: "Gavin Bierman" <gavin.bierman at oracle.com>
>> To: "amber-spec-experts" <amber-spec-experts at openjdk.java.net>
>> Sent: Wednesday, February 9, 2022 12:59:02 PM
>> Subject: JEP 405 update
> 
>> Dear experts,
>> 
>> Just to let you know that I have updated JEP 405:
>> 
>> https://openjdk.java.net/jeps/405
>> 
>> You will see that we have removed the array patterns from this JEP (and it has
>> been retitled accordingly). We're still committed to supporting a direct pattern
>> form for arrays, but given our tight schedule and a number of queries about the
>> exact syntactic form for array patterns, we think we'll be better off decoupling
>> them from JEP 405, and releasing them in a future patterns JEP.
>> 
>> Comments welcomed!
>> Gavin