RFC: draft API for JEP 269 Convenience Collection Factories

[Remi Forax]

Hi Stephen,
you can use Arrays.setAll() which do something similar.

The code seems really simple,
  public static <T> List of(int size, IntFunction<T> valueFunction) {
    T[] array = (T[])new Object[size];
    Arrays.setAll(array, valueFunction);
    return List.of(array);
  }
or I miss something ?

Rémi

----- Mail original -----
> De: "Stephen Colebourne" <scolebourne at joda.org>
> À: "core-libs-dev" <core-libs-dev at openjdk.java.net>
> Envoyé: Jeudi 15 Octobre 2015 16:28:00
> Objet: Re: RFC: draft API for JEP 269 Convenience Collection Factories
> 
> I've been working on a Java 8 wrapper class around double[] in my day
> job, and added the following factory method:
> 
>   /**
>    * Obtains an instance with entries filled using a function.
>    * <p>
>    * The function is passed the array index and returns the value for
> that index.
>    *
>    * @param size  the number of elements
>    * @param valueFunction  the function used to populate the value
>    * @return an array initialized using the function
>    */
>   public static DoubleMatrix1D of(int size, IntToDoubleFunction
>   valueFunction) {
>     if (size == 0) {
>       return EMPTY;
>     }
>     double[] array = new double[size];
>     for (int i = 0; i < array.length; i++) {
>       array[i] = valueFunction.applyAsDouble(i);
>     }
>     return new DoubleMatrix1D(array);
>   }
> 
> View on GitHub here:
> https://github.com/OpenGamma/Strata/commit/63e73652194a3dd94e37fbc407f4933c10abadda#diff-2a9787868cf0654b4a6a07e75c1a6286R199
> 
> It occurs to me that it would be a *very* good idea to add a similar
> method to List.
> 
> public static <T> List of(int size, IntFunction<T> valueFunction) { ... }
> 
> Stephen
> 
> 
> 
> On 14 October 2015 at 11:39, Stephen Colebourne <scolebourne at joda.org> wrote:
> > On 14 October 2015 at 10:38, Paul Sandoz <paul.sandoz at oracle.com> wrote:
> >>> On 14 Oct 2015, at 06:18, Stuart Marks <stuart.marks at oracle.com> wrote:
> >>> I'm not entirely sure what to take from this. If it were clearly
> >>> exponential, we could say with confidence that above a certain threshold
> >>> there would be vanishingly little benefit adding more arguments. But
> >>> since the curve seems to flatten out, maybe this is pushing us to add
> >>> more pairs than we had originally thought. The current draft API has 8
> >>> pairs; that seems to leave a few percent of cases on the table.
> >>> Obviously we can't get to 100%, but is 97% good enough?
> >
> > I'd say 5 is definitely too little, without an easy builder fallback
> > (as Guava provides). I'd say the right number is between 8 and 10.
> >
> > Stephen
>