JEP 301: Enhanced Enums

[forax at univ-mlv.fr]

----- Mail original -----
> De: "John Rose" <john.r.rose at oracle.com>
> À: forax at univ-mlv.fr
> Cc: "Maurizio Cimadamore" <maurizio.cimadamore at oracle.com>, platform-jep-discuss at openjdk.java.net
> Envoyé: Jeudi 8 Décembre 2016 22:12:14
> Objet: Re: JEP 301: Enhanced Enums

> On Dec 7, 2016, at 11:23 PM, forax at univ-mlv.fr wrote:
>> 
>> Name functions are not useful anymore, because now we have full real lambdas.
> 
> There is still a big place for named function enums. Lambdas let you say "here
> is a plus operator" but not "here is the plus operator which is abelian with
> unit 0". Enums can fill that gap, for now.

you mean something like:
  interface Group<T> {
    BinaryOperator<T> binOp();
    T identity();
    boolean is(Characteritics characteristics);
    ..
  }

  enum Op<T> implements Group<T> {
    PLUS<Integer>(Integer::sum, 0, Characteritics.ABELIAN)
    ;
    ...
  }

  public static <T> Optional<T> reduce(List<? extends T>list, Group<T> group) {
    if (group.is(Characteritics.ABELIAN) && list.size() > ...) {
      return Optional.of(parallelReduce(list, group.identity(), group.binOp())); 
    }
    return foldLeft(list, group.binOp());
  }
  ...
  reduce(List.of(1, 2, ...), Op.PLUS);


but you can simply write

static class Op<T> implements Group<T> {
  public static final Group<Integer> PLUS = new Op(Integer::sum, 0, Characteritics.ABELIAN);
  ...
}  

> 
> – John

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