Fwd: Java records used in enums

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---------- Forwarded message ---------
From: - <liangchenblue at gmail.com>
Date: Fri, May 21, 2021 at 10:14 AM
Subject: Re: Java records used in enums
To: Alberto Otero Rodríguez <albest512 at hotmail.com>


I fail to understand what you want. How does making enums records fix the
multithreading issue?

If you wish to have enums declared like records code-wise, I see it as a
possibility, but I don't see how it affects any enum behavior in any way.

If you want a combination of record and enum, or a record with enumerated
possible instances, it may be possible to add an alternative syntax for
such enum declaration; but restricting all enums to be such enum records
offers no benefit that I can see, especially given records themselves have
severe restrictions (must have an accessible canonical ctor available; that
ctor cannot throw checked exceptions; field/getter method name limits, so a
"enum record" cannot declare fields like "values" "name"); also records are
value-based while enums are identity based, which is another problem.

In short, I believe regular enum suffices and a "record enum" offers little
benefit while it cannot fix your issue at all.

On Fri, May 21, 2021 at 10:00 AM Alberto Otero Rodríguez <
albest512 at hotmail.com> wrote:

> It seems a non-existent problem until you face it, which is what happened
> me today.
>
> I think at least (supposing enums can't be records) all the fields in
> enums should be made final by default.
>
> Regards,
>
> Alberto.
> ________________________________
> De: Kasper Nielsen <kasperni at gmail.com>
> Enviado: viernes, 21 de mayo de 2021 16:28
> Para: Alberto Otero Rodríguez <albest512 at hotmail.com>
> Cc: core-libs-dev at openjdk.java.net <core-libs-dev at openjdk.java.net>
> Asunto: Re: Java records used in enums
>
> On Fri, 21 May 2021 at 14:51, Alberto Otero Rodríguez <
> albest512 at hotmail.com<mailto:albest512 at hotmail.com>> wrote:
> Hi,
>
> I think enums in Java should be immutable. When you let the programmer
> change values in an enum instance, an unexpected behaviour can happen when
> using multiple threads as enum instances are static (singleton).
>
> So, I was wondering why not make enums instances be defined as records
> instead of normal classes.
>
> Lots of reasons, for example:
> * It would be a breaking change for an almost non-existent problem.
> * All internal state of enums would now be public.
> * Enum's extend java.lang.Enum, records extend java.lang.Record.
>   java.lang.Enum cannot extend java.lang.Record because it has instance
> fields.
>
> /Kasper
>