RFR: 8351565: Implement JEP 502: Stable Values (Preview) [v6]

[Per Minborg]

On Tue, 25 Mar 2025 14:20:24 GMT, Luca Kellermann <duke at openjdk.org> wrote:

>>> Comments on visual noise and side effects in `toString`.
>>> 
>>> `renderWrapped` is clever for a single stable value, but it makes for a very noisy display string, with confusing doubly-nested `[]`, for composite stable values. I'm talking about `StableFunction` mainly, I guess.
>>> 
>>> I suggest omitting the inner `[]` for such composites. A simple boolean on `renderWrapped` will do that trick. In that case, `renderWrapped` has the job of either presenting a fixed (recognizable) sentinel string, or else forwards, without further editorial comment, to the `toString` of the contained value.
>> 
>> The `toString()` for `StableValue` is inspired by `Optional` which works in the same way by adding `[ ]` around the contents. Any more thought in the reviewer community on how we should handle this?
>
>> > Comments on visual noise and side effects in `toString`.
>> > `renderWrapped` is clever for a single stable value, but it makes for a very noisy display string, with confusing doubly-nested `[]`, for composite stable values. I'm talking about `StableFunction` mainly, I guess.
>> > I suggest omitting the inner `[]` for such composites. A simple boolean on `renderWrapped` will do that trick. In that case, `renderWrapped` has the job of either presenting a fixed (recognizable) sentinel string, or else forwards, without further editorial comment, to the `toString` of the contained value.
>> 
>> The `toString()` for `StableValue` is inspired by `Optional` which works in the same way by adding `[ ]` around the contents. Any more thought in the reviewer community on how we should handle this?
> 
> I think the comment just proposes that this code
> 
> var f = StableValue.intFunction(3, i -> i);
> f.apply(1);
> System.out.println(f);
> 
> should print
> 
> StableIntFunction[values=[.unset, 1, .unset], original=...]
> 
> Right now it prints this:
> 
> StableIntFunction[values=[.unset, [1], .unset], original=...]
> 
> The `toString` implementation for `StableValueImpl` itself seems fine.

Thank you, @lukellmann, for your comments. Some of them were very useful! I will address them _after_ integrating the PR.

-------------

PR Comment: https://git.openjdk.org/jdk/pull/23972#issuecomment-2830400309