Draft JEP Announcement: "Computed Constants"

[Per-Ake Minborg]

Hi Rémi,

I share your view that it is important to be able to use ComputedConstant "early" in the VM startup sequence. There is nothing inherent to the proposed API that *requires* a lambda or a method reference to be used. An anonymous or regular class, implementing Supplier would also do. Also, there is nothing fundamental that prevents us from *implementing* the API in a way it can be used "early".

We do not add any keywords, the JEP is a pure library approach so, I do not foresee any backward compatibility issues.

Thanks for your feedback.

Best, Per
________________________________
From: forax at univ-mlv.fr <forax at univ-mlv.fr>
Sent: Thursday, July 27, 2023 6:36 PM
To: Maurizio Cimadamore <maurizio.cimadamore at oracle.com>
Cc: Per-Ake Minborg <per-ake.minborg at oracle.com>; leyden-dev <leyden-dev at openjdk.org>; John Rose <john.r.rose at oracle.com>
Subject: [External] : Re: Draft JEP Announcement: "Computed Constants"



________________________________
From: "Maurizio Cimadamore" <maurizio.cimadamore at oracle.com>
To: "Remi Forax" <forax at univ-mlv.fr>, "Per-Ake Minborg" <per-ake.minborg at oracle.com>
Cc: "leyden-dev" <leyden-dev at openjdk.org>, "John Rose" <john.r.rose at oracle.com>
Sent: Thursday, July 27, 2023 6:14:48 PM
Subject: Re: Draft JEP Announcement: "Computed Constants"

Hi Remi
Yes, of course we were aware of that.

Think of this proposal as an API-driven approach (in the style of ThreadLocal, ClassValue, ScopedValue, ...) which delivers more or less the same feature, but w/o changing the language.


One thing that's attractive about the API approach is that it is not limited to just static fields, but it can also work for instance fields as well.


(that said, I agree the two jeps should somehow be related/link to each other)

I see two problems with your suggested approach:
- this proposal is on top of lambdas, which means that it can be used for applications but not for the VM startup because it can only be used after method handles sub-system have been initialized.
- this is not a backward compatible change, if you add a new keyword to static final fields, you can rewrite any public static final fields to a public lazy static final field,
  by example, String.CASE_INSENSITIVE_ORDER which is rarely used but can not be changed with your proposal.


Maurizio

Rémi



On 27/07/2023 17:09, Remi Forax wrote:
Hello,
Are you aware of the lazy static final fields proposal ?
  https://bugs.openjdk.org/browse/JDK-8209964

In think both proposals should be merged.

Rémi

________________________________
From: "Per-Ake Minborg" <per-ake.minborg at oracle.com><mailto:per-ake.minborg at oracle.com>
To: "leyden-dev" <leyden-dev at openjdk.org><mailto:leyden-dev at openjdk.org>
Sent: Thursday, July 27, 2023 5:52:46 PM
Subject: Draft JEP Announcement: "Computed Constants"
Hi all,

  Maurizio and I have drafted a JEP for computed constants, which are
  immutable value holders that are initialized at most once.  They offer
  the performance and safety benefits of final fields while offering
  greater flexibility as to the timing of initialization.  In the
  context of Leyden, they could be one basis for shifting computation
  both forward and backward in time.

  The draft is here:https://openjdk.org/jeps/8312611

  Now that the Leyden repo is open, I’ll publish the prototype code to a
  new branch there shortly.

  Comments are welcome!

  Best, Per



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