Is V? what we need ?

Remi Forax forax at
Wed May 1 14:52:33 UTC 2019

you are more on my side because what i'm proposing make V? less present in public methods of API, which i think is a good move in term of perf model and for ArryList<N?>, both proposal work the same.


----- Mail original -----
> De: "Doug Lea" <dl at>
> À: "valhalla-spec-experts" <valhalla-spec-experts at>
> Envoyé: Mercredi 1 Mai 2019 16:32:18
> Objet: Re: Is V? what we need ?

> On 5/1/19 10:12 AM, Brian Goetz wrote:
>> You’re assuming the utility of V? after reification is zero, but
>> that’s not the case. For example, suppose ArrayList is reified.  Then
>> the user gets the choice of erasure or reification by selecting
>> ArrayList<V?> or ArrayList<V>. Erasure has a bad rap, but sometimes
>> it is desirable.
> As I tried but failed to get across in post on sorting, choosing V vs V?
> can lead to 5X cost differences in *either direction* for common
> aggregate (collection and array) operations. So programmers will need to
> learn some of these consequences. (Which is made harder/worse here
> because the cost tradeoffs will probably change over time as VM support
> improves.)
> Which is mainly an argument for Brian's position, except for those who
> believe that Java programmers should not have to encounter these kinds
> of issues that C++, C#, OCAML, etc programmers face all the time;
> betting that somehow VMs will make the right choice.
> (Maybe this is not the right time to mention this, but most other
> languages supporting this range of use have a middle-ground of
> call-by-ref for extracting small parts of large things, as seen in
> comparators, hash-codes, etc that can make a big performance difference.
> I expect people will complain about not supporting this.)
> -Doug

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