New Collections interface - Sized

[Remi Forax]

----- Mail original -----
> De: "Stephen Colebourne" <scolebourne at joda.org>
> À: "core-libs-dev" <core-libs-dev at openjdk.java.net>
> Envoyé: Samedi 24 Avril 2021 00:14:51
> Objet: Re: New Collections interface - Sized

> On Fri, 23 Apr 2021 at 23:07, Brian Goetz <brian.goetz at oracle.com> wrote:
>> >> Is there a compelling example of where this would be used by clients?
>> > Here are some examples:
>> > https://stackoverflow.com/questions/10988634/java-global-isempty-method
>> Without passing judgment on the sort of dynamically typed programs that
>> need a method like this
> 
> The other example is better as it benefits from declaring an API that
> only accepts instances of `Sized` and does not need to get the
> contents.
> 
>> But again, if you are treating these things as containers, then a Sized
>> doesn't get you very far, because if you conclude the thing isn't empty,
>> you're going to want to get stuff out, and Sized has no methods for
>> that.  So presumably there's some companion to Sized for accessing
>> elements by index:
>>
>>      interface HasStuff<T> extends Sized {
>>          T get(int index);
>>      }
> 
> I don't think there has to be. the more useful interface would be this
> one, but to date there has been strong resistance in unifying the
> Collection and Map interfaces:
> 
>     interface Stuff<T> extends Sized {
>         int size();
>         int isEmpty();
>         int isNotEmpty();
>        Iterator<t> iterator();
>     }

This is basically Spliterator, an iterator + a size, with the iterator is "push" instead of "pull" because it's more efficient.

In details a Spliterator is either
- an Iterable (with no SIZED characteristic)
- an Iterable + size (if SIZED and estimateSize() != Long.MAX_VALUE)
- an Iterable + comparator (if SORTED and comparator != null)
- an Iterable + split (if trySplit != null)

and all combinations of the above.

> 
> Stephen

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