JDK-8317277 - Java language implementation of value classes and objects

[Archie Cobbs]

On Wed, Oct 18, 2023 at 3:59 PM Remi Forax <forax at univ-mlv.fr> wrote:

>
> 1. If v is a value object, what does System.identityHashCode(v) return?
>
>
> A combination of some field values of the object.
> It has to be fast so the VM should not use all fields if there are a lot
> of them or if some values are value class (or field type that can
> potentially store value class) because it will make the computation
> recursive.
>

Hmm, that doesn't seem right.

Isn't it hashCode()'s job to produce a value based on the object's fields?
The whole point of System.identityHashCode() is to NOT do that, at least as
of today.

I'd expect System.identityHashCode() to return 0 for all value classes or
throw an exception.

After all, value classes are not supposed to have an identity, right?


> 2. If V is a value class, is {Weak,Soft,Phantom}Reference<V> supported?
>
>
> Nope. There is maybe no address/no pointer so no weak reference.
>

OK. How is this going to be enforced?

-Archie

-- 
Archie L. Cobbs
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