where are all the objects?

[Brian Goetz]

And now to your other thread:

On 8/10/2022 1:38 PM, Kevin Bourrillion wrote:
>
> The VANO model does a lot of "doubling down" on the distinctions 
> between objects and values, which does have a certain "stuck in the 
> past" feeling to it. A benefit is "concreteness" and a feeling that 
> "there is plenty of solid ground under your feet that Valhalla is not 
> pulling out from under you". That feeling is important to me, 
> particularly because developers in the real world will regularly find 
> themselves going back and forth between pre-valhalla and post-valhalla 
> code for a very long time. A hazard is that it equips developers to 
> care more about that distinction that they really should *moving 
> forward*, particularly since the VM is a cheating cheater. Essentially 
> we're saying "for understanding, you can lean on what you know about 
> int-vs-Integer, but now understand why the distinction will matter 
> less and less to you."
>
> (John associates VANO with "boxes and arrows". I think that's right 
> and good? It seems called for because an /arrow/ is the thing that 
> could be null instead.)
>
> The VAO model does seem more forward-thinking. Why should we invest in 
> the question of when exactly objects "exist" or not when those objects 
> can't be programmatically distinguished from each other anyway, nor 
> from their corresponding values?
>
> The eventual "final" presentation of value classes to users (in the 
> permanent documentation and the definitive seminal slide 
> presentations, and to *some* degree in the JLS itself) should anchor 
> on one model or the other. But these docs/presentations might also 
> want to say "and here's why you get to think of it this other way when 
> you want to". That may sound like trying to have it both ways, but... 
> I want to believe that as long as one is subjugated to the other it 
> would be fine. "Here's how little is *really* changing; here's how 
> your day-to-day modell gets to evolve because of that".
>

The VAO model says:

  - classes have instances, which are objects
  - An object _reference_ can refer to any object, identity or value
  - A value object can also be represented directly, as primitives are 
today   // (*)
  - We've unified under "everything is an object", but added: not all 
objects require references

The uncomfortable part of this model is that while we are familiar with 
the notion marked (*), because of primitives, we don't really have a 
good name for it.  So part of this is that there much bumbling and 
fumfering around phrases like "represented directly" and "bare" and 
other made-up words that we have to say "but but it's just like what you 
know about primitives."

The VANO model says:

  - classes have instances, but not all instances are objects. some are 
values instead
  - Each value class V gets a special box class V.ref, which has a 
single field of type V.val, like the boxes we know
  - The boxing and unboxing conversions, though, are super fast! Because 
they're not burdened by identity preservation
  - We've unified under "everything is a class instance" and kept "all 
objects require references", and the spirit (but not performance) of boxes

My intuition is that if we can come up with a better term for 
"represented directly" that doesn't feel forced, the things we dislike 
about VAO will be lessened and its unification under "everything is an 
object" will win the day.

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