flatMap signature (original) (raw)

Boaz Nahum boaznahum at gmail.com
Tue Apr 2 05:44:34 PDT 2013

Stream:

As Brian correct me: Stream flatMap(Function<? super T, ? extends Stream<? extends R>> mapper);

instead of: Stream flatMap(Function<T, Stream<? extends R>> mapper);

T reduce(T identity, BinaryOperator accumulator); and Optional reduce(BinaryOperator accumulator);

Can't be fixed because they used 'BinaryOperator', But if 'BiFunction' is used then we have more flexibility

U reduce(U identity, BiFunction<? super U, ? super T, ? extends U> accumulator, BinaryOperator combiner)

Instead of:

U reduce(U identity, BiFunction<U, ? super T, U> accumulator, BinaryOperator combiner);

Same comment regarding 'BinaryOperator'

R collect(Supplier resultFactory, BiConsumer<? super R, ? super T> accumulator, BiConsumer<? super R, ? super R> combiner)

Instead of:

<R> R collect(Supplier<R> resultFactory,
              BiConsumer<R, ? super T> accumulator,
              BiConsumer<R, R> combiner);

I tested all my suggestions with examples and pseudo implementation, example:

default U reduce(U identity, BiFunction<? super U, ? super T, ? extends U> accumulator, BinaryOperator combiner) {

        Collection<T> _this = ....

        U result = identity;

        for (T element : _this)
               result = accumulator.apply(result, element);

        return combiner.apply(identity, result);

    }

If you find my comments useful, I will be more than glad to continue on other API.

On Mon, Apr 1, 2013 at 1:32 PM, Remi Forax <forax at univ-mlv.fr> wrote:

On 03/31/2013 05:10 PM, Boaz Nahum wrote: > I have some problems when compiling with flatMap, > > Maybe the signature should be: > > Stream flatMap(Function<? super T, Stream<? extends R>> mapper); > > Instead of: > > Stream flatMap(Function<T, Stream<? extends R>> mapper); >

yes, probably, I will do a pass on the whole API to fix all wildcards, if you or anybody on this list want to help me, it would be great. cheers, Rémi

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