[External] : Re: JEP 447 Statements before super() - Preview feature?

[Archie Cobbs]

Hi Alex,

Great comments, thanks....

On Thu, May 18, 2023 at 2:25 PM Alex Buckley <alex.buckley at oracle.com>
wrote:

> ... the Non-Goals should focus on what the end user (a developer) will
> see or not see. Finally, almost no-one will be able to figure out what
> this means -- "There are many ways in which the interplay between
> superclass constructors and subclass initialization might be improved"
> -- so please either explain (in a very small space) or remove.
>

Agreed - removed.

I'm saying that millions of lines of code exist because people explicitly
> coded around the restriction you're now removing, so there's a huge
> amount of refactoring that is (a) possible and (b) desirable, so we
> _assume_ that static analyzers and IDEs will promote this refactoring to
> their users. If you don't say this in the JEP, no-one will know it.
> No-one knows as much as you about this feature, so please share :-)
>

Good point.. I've added some more verbiage to Risks & Assumptions.

 I also added some language to highlight the fact that this
"pre-construction" context we are creating is not really new - the rules
are the same as already apply to the this()/super() parameter expressions.

So hopefully that is a big hint to any tool providers that they already
know how to treat the code in the constructor prologue.


> I would like to enrich the "Implementing fail-fast" subsection by
> acknowledging the fine idiom of _telescoping constructors_, where
> simpler constructors delegate to richer constructors by using `this(..)`
> to pass default arguments (see https://stackoverflow.com/a/285187). In
> any intermediate constructor of non-zero arity, being able to check the
> arguments before delegation could be useful.
>

"Telescoping constructors" is definitely a worthy use case for this
feature... I like that and have added it.

And a good real-world example comes from none other than java.lang.Thread.

-Archie

-- 
Archie L. Cobbs
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