Draft JEP Announcement: "Computed Constants"

[forax at univ-mlv.fr]

> From: "Brian Goetz" <brian.goetz at oracle.com>
> To: "Per-Ake Minborg" <per-ake.minborg at oracle.com>, "Remi Forax"
> <forax at univ-mlv.fr>, "Maurizio Cimadamore" <maurizio.cimadamore at oracle.com>
> Cc: "leyden-dev" <leyden-dev at openjdk.org>, "John Rose" <john.r.rose at oracle.com>
> Sent: Friday, July 28, 2023 5:06:07 PM
> Subject: Re: Draft JEP Announcement: "Computed Constants"

>> 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.

> Allow me to translate ...

> Remi was assuming a goal. The problem is that he didn't state that goal, or his
> assumption that this was a goal, before jumping to criticizing your proposal.
> As a result, his criticism was unclear, and IMO misplaced.

> The hidden goal that Remi was assuming is that "it should be possible to migrate
> existing code that uses static final fields to use computed constants in a
> source- and binary-compatible way." Now, it should have been entirely clear
> from content that this was a non-goal of this JEP (you didn't propose a
> language or VM solution, and that was clearly deliberate), and if he wanted to
> express his disappointment, he should have done so more directly, such as "I
> wish there was a way to let old code play in this game." To which the answer
> would have been "We may get there someday, some day, but we're starting with
> something simpler."
You are making the assumption that you can not have both, a binary-compatible way of moving things out of the static init block and a solution not based on a keyword. 
I do not think this is true. 

In my opinion, what this JEP got right is to try to tag what can be moved out of a static init block, making the job of a condenser easier. 
But this JEP still allows 
- any codes to create a ComputedConstant, you can create a ComputedConstant from the content of a HTTP request, 
- a ComputedConstant can be part of the API (public field), so it can not be elided, 
- multiple fields to be initialized by one ComputedConstant. 
All those things are making the implementation of a condenser far harder than it should. 

But i'm sure, i'm wrong and there is already a written condenser somewhere that shows that i'm just a naysayer not able to see how simple the ComputedConstant API really is. 

Rémi 
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