[External] : Re: Draft JEP Announcement: "Computed Constants"

[Per-Ake Minborg]

Sorry for being unclear.

So, the API guarantees evaluation is made at most once, so it is an error to recursively invoke a value provider (which value would we then bind?). Consequently, there are no plans to allow circular evaluation.

However, you can check if another ComputedConstant isBound() from a provider for another ComputedConstant. It is also allowed to get() the bound value from other ComputedConstants as long as they do not query the querying ComputedConstant instance. For example, you might want to have a List<ComputedConstant<Integer>> that caches the Fibonacci series and when computing fib(n), you invoke fib(n-1) and fib(n-2) as the latter do not invoke fib(n).

I hope that clears things up.

Best, Per
________________________________
From: David Alayachew <davidalayachew at gmail.com>
Sent: Monday, July 31, 2023 10:30 AM
To: Per-Ake Minborg <per-ake.minborg at oracle.com>
Cc: leyden-dev at openjdk.org <leyden-dev at openjdk.org>
Subject: Re: [External] : Re: Draft JEP Announcement: "Computed Constants"

Hello Per,

Thank you for the response!

I'm afraid I don't follow. Could you demonstrate what you mean?

Thank you for your time and help!
David Alayachew

On Mon, Jul 31, 2023 at 3:05 AM Per-Ake Minborg <per-ake.minborg at oracle.com<mailto:per-ake.minborg at oracle.com>> wrote:
Hi David.

Thanks for the encouragement.

You can actually *reference* CC objects in a circular way as long as you do not create circularity in the *evaluation* of CC objects. So, it is, for example, perfectly legal to query if a CC is bound via the isBound() method in a circular way.

Just to remind you, initialization can only be made at most once per CC instance/element.

Best, Per
________________________________
From: David Alayachew <davidalayachew at gmail.com<mailto:davidalayachew at gmail.com>>
Sent: Thursday, July 27, 2023 7:27 PM
To: Per-Ake Minborg <per-ake.minborg at oracle.com<mailto:per-ake.minborg at oracle.com>>
Cc: leyden-dev at openjdk.org<mailto:leyden-dev at openjdk.org> <leyden-dev at openjdk.org<mailto:leyden-dev at openjdk.org>>
Subject: [External] : Re: Draft JEP Announcement: "Computed Constants"

Hello Per,

Thank you for posting this JEP!

It looks great. The solution is concise, clear, and simple, and any complaints I have about verbosity can be mostly addressed with var. And that list suggestion was especially nice. That's very neat.

I'd like to ask about the safety point. I certainly understand the reason why it exists -- some developers will inadvertently create a circular reference and end up causing problems.

However, I see a lot of utility for circular references too. Any chance that we could allow devs to opt-in to circular references?

Earlier this month, I started 2 threads that were broaching the subject of a very similar pain point to this one. Here they both are.

https://mail.openjdk.org/pipermail/amber-dev/2023-July/008129.html

https://mail.openjdk.org/pipermail/amber-dev/2023-July/008154.html

I'm curious how this Computed Constant solution would work out for the problem I have. But in order for it to work, it would need to enable circular references, hence my question.

But even without it, I see a lot of utility for this tool. I'm excited to get to work prototyping with it.

Thank you for your time and help!
David Alayachew
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