Anonymous classes of enum constants and var

[David Alayachew]

I was extremely extremely sad when they said no JEP 301. 🥺

Enums would be literally perfect if we had that feature. And Java enums are
so much better than literally any other non-JVM languages enums, so part of
me also wishes we could widen the gap further lol.

And to clarify, when I say the word enum, I am referring to an enumerated
set of VALUES, not TYPES. Rust and friends like to use enums to do types,
which is not the same thing. That's more like our sealed types.

But as far as enum of values, we are uncontested, save for other JVM
languages.

On Wed, Feb 21, 2024, 9:27 AM Tagir Valeev <amaembo at gmail.com> wrote:

> There's a withdrawn JEP 301 which tried to address this issue, among other
> things (see "Sharper typing of enum constants" section):
> https://openjdk.org/jeps/301
>
> Unfortunately, this was never implemented due to issues in the part that
> suggested making enums generic. I'm not aware of issues in "sharper typing"
> alone (without the "generic" feature). Probably it could be done
> separately, but likely nobody wants to invest resources in this.
>
> With best regards,
> Tagir Valeev.
>
> On Wed, Feb 21, 2024 at 1:14 PM Pavel Rappo <pavel.rappo at oracle.com>
> wrote:
>
>> From https://mail.openjdk.org/mailman/listinfo/discuss, this mailing
>> list is not suitable for questions like this. I'm not sure which mailing
>> list is *the most* suitable, but the following one is surely more suitable:
>> https://mail.openjdk.org/pipermail/amber-dev/ (CC'ed).
>>
>> I believe, the reasons why the first snippet of yours works, but the
>> second doesn't, is covered here:
>>
>>   *
>> https://docs.oracle.com/javase/specs/jls/se21/html/jls-8.html#jls-8.9.1
>> (like you said)
>>   *
>> https://docs.oracle.com/javase/specs/jls/se21/html/jls-14.html#jls-14.4.1
>>
>> I would be surprised if that could change to allow your second snippet.
>> That said, if that functionality is truly required, you can provide it
>> yourself.
>>
>> The design of enums allows you to declare a method on an enum class and
>> then override it in a particular constant. Alternatively, you can switch on
>> an enum constant to provide constant-specific behaviour "externally".
>>
>> -Pavel
>>
>> > On 21 Feb 2024, at 10:08, Red IO <redio.development at gmail.com> wrote:
>> >
>> > I recently tinkered a bit with java enums. While I was researching edge
>> features enums support I came across a stackoverflow post referencing the
>> JLS 8.9 saying that the optional body of an enum constant is an anonymous
>> class declaration.
>> > As for some time now methods declared in an anonymous class assigned to
>> a var variable are accessible I tried to do the same for the enum constant.
>> >
>> > var anonymous = new Object() {
>> > public void test() {}
>> > }
>> > anonymous.test(); //works
>> >
>> >
>> > enum Test {
>> > A {
>> > public void test() {}
>> > }
>> > }
>> > var enumConstant = Test.A;
>> > enumConstant.test(); // doesn't work
>> >
>> > I have a clue to why this doesn't work. It's likely that the type of
>> the constant A is the type of the enum and not of the anonymous class.
>> >
>> > There are some usecases where exclusive methods on enum constants might
>> be useful. So it would be nice if this would work.
>> >
>> > Great regards
>> > RedIODev
>> >
>> >
>> >
>> >
>>
>>
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