JEP proposed to target JDK 11: 323: Local-Variable Syntax for Lambda Parameters

[forax at univ-mlv.fr]

> De: "Jonathan Bluett-Duncan" <jbluettduncan at gmail.com>
> À: "Remi Forax" <forax at univ-mlv.fr>
> Cc: "jdk-dev" <jdk-dev at openjdk.java.net>
> Envoyé: Lundi 29 Janvier 2018 01:02:52
> Objet: Re: JEP proposed to target JDK 11: 323: Local-Variable Syntax for Lambda
> Parameters

> Hi Rémi,

> You may find my (short) response inline.

Hi Johnathan, 

> On 28 January 2018 at 23:47, Remi Forax < [ mailto:forax at univ-mlv.fr |
> forax at univ-mlv.fr ] > wrote:

>> Hi Andrew,

>> ----- Mail original -----
>> > De: "Andrew Haley" < [ mailto:aph at redhat.com | aph at redhat.com ] >
>>> À: "Zheka Kozlov" < [ mailto:orionllmain at gmail.com | orionllmain at gmail.com ] >,
>>> "Martijn Verburg" < [ mailto:martijnverburg at gmail.com |
>> > martijnverburg at gmail.com ] >
>> > Cc: "jdk-dev" < [ mailto:jdk-dev at openjdk.java.net | jdk-dev at openjdk.java.net ] >
>> > Envoyé: Vendredi 26 Janvier 2018 16:09:34
>>> Objet: Re: JEP proposed to target JDK 11: 323: Local-Variable Syntax for Lambda
>> > Parameters

>> > On 26/01/18 09:59, Zheka Kozlov wrote:
>> >> The motivation is to allow `final` and annotations on lambda parameters:

>> >> (final var x) → x + 1;
>> >> (@Nonnull var x) → x + 1;

>> > I'm trying to understand how it makes sense to have something
>> > that's both variable and final.

>> yes, 'final var' is an odd combination, 'var' means more this is a local
>> variable and less this is something which is variable.

>> In Java, you can declare a parameter of a method final which means it's a local
>> variable that can be only assigned once, given that parameters are assigned
>> with the calling arguments, it means that this parameter can not be
>> re-assigned. This is just a compile time 'annotation', because marking a
>> parameter or a local variable final is not something which is stored in the
>> classfile (apart if you compile with the -parameters, but most people don't).

>> Some coding conventions, mostly the one from Google mandates that all method
>> parameters are declared final, so since Java 8, some developers have asked to
>> be able to declare lambda parameters final.

> Oh, do Google's coding conventions really mandate this practice? I've had a look
> through the Google Java Style guide, but I can't seem to find anything to
> confirm it. Do you have a source that I can check?

Ok, this reply enters in the category of "never post after 1am", so i apologize, i should have checked the resources online before saying something stupid, 
i've seen code written by Googlers and ex-Googlers and from that i've stupidly thunk that it was Google thing. 

Actually, it's worst, after a quick search on the internet, it seems to be a checkstyle rule enables by default, not something written in a guide. 

>> In a perfect World, Google should update its coding convention because mandating
>> to declare local variables final has the nasty side effect of blurring the
>> distinction between final for a field which as you know has effects defined by
>> the memory model and final on local variable which has no effect. So mandating
>> to declare local variables final is harmful.


>> > --
>> > Andrew Haley
>> > Java Platform Lead Engineer
>> > Red Hat UK Ltd. < [ https://www.redhat.com/ | https://www.redhat.com ] >
>> > EAC8 43EB D3EF DB98 CC77 2FAD A5CD 6035 332F A671

>> cheers,
>> Rémi

> Cheers,
> Jonathan

regards, 
Rémi