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

[Luca Kellermann]

On Fri, 21 Mar 2025 16:19:17 GMT, Per Minborg <pminborg 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?

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.

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PR Comment: https://git.openjdk.org/jdk/pull/23972#issuecomment-2751428512