Scope for JEP 468: Derived record creation

[Brian Goetz]

While such a feature is possible, I am not particularly excited about it 
for several reasons.  If the goal is "I want to construct using named 
instead of position arguments" (which I think is your goal), it's a 
pretty verbose syntax; a better one would be

     new R(a: 1, b: 2)

But that's a much smaller concern.  The bigger one is that I don't think 
the language is improved by having a named parameter mechanism for 
records, but for nothing else (not for instantiating class instances, 
not for invoking methods.)  While it might seem "better than nothing", 
having two different ways to do something, but one of them only works in 
narrow situations, is as likely to be frustrating than beneficial.  If 
the payoff is big enough, then it might be a possibility, but 
"invocation by parameter name" is nowhere near that bar.

Finally, if it works for records but not for classes, it makes it harder 
to refactor from records to classes, since there will be use sites that 
have to be adjusted.

So I think for the time being, the answer is "no", though if we run out 
of things to work on, we might reconsider.


On 2/29/2024 4:34 PM, Swaranga Sarma wrote:
> The JEP looks really promising. However I am wondering if there will 
> be a separate JEP for creating new records from scratch with similar 
> syntax.
>
> The current JEP states that its goals are to enable creating records 
> from an existing record and for that it seems sufficient. But I would 
> also love to be able to create new records from scratch using the same 
> syntax. Something like:
>
> var circle = new Circle with {
>   radius = 0.5f;
>   center = new Center with {
>     x = 0;
>     y = -1;
>     z = 8;
>   };
> };
>
> Originally I had asked Brian Goetz about record literals and they 
> seemed like a possibility but withers seem like a more general feature 
> so I am hoping something like this would be supported in the future.
>
> Regards
> Swaranga Sarma
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