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

[Alex Buckley]

Hi Archie,

Your updates to the JEP are excellent in every way. Thank you.

Alex

On 5/18/2023 3:56 PM, Archie Cobbs wrote:
> Hi Alex,
> 
> Great comments, thanks....
> 
> On Thu, May 18, 2023 at 2:25 PM Alex Buckley <alex.buckley at oracle.com 
> <mailto: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
>     <https://urldefense.com/v3/__https://stackoverflow.com/a/285187__;!!ACWV5N9M2RV99hQ!O-9cBnMpSBttTFUwyTA_mphXNEnUrb691HNu5nTJkieZQZMkA1UgNTyTpWa05uE-RnIz8ZnI_-8soiSv_GkKYHs1Sw$>). 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