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

[Jonathan Bluett-Duncan]

Hi Rémi,

You may find my (short) response inline.

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

> Hi Andrew,
>
> ----- Mail original -----
> > De: "Andrew Haley" <aph at redhat.com>
> > À: "Zheka Kozlov" <orionllmain at gmail.com>, "Martijn Verburg" <
> martijnverburg at gmail.com>
> > Cc: "jdk-dev" <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?


>
> 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>
> > EAC8 43EB D3EF DB98 CC77 2FAD A5CD 6035 332F A671
>
> cheers,
> Rémi
>

Cheers,
Jonathan