FlatMapper (original) (raw)

Zhong Yu zhong.j.yu at gmail.com
Tue Feb 12 11:19:18 PST 2013

One common use case is to map zero or more elements in stream A into one element in stream B. People can, and will, use flatMap(FlatMapper) to achieve that (with a side effecting mapper), even though it is the opposite of what "flat map" was known for. I think the method could use a more general name which is appropriate for both explode/implode.

Another use case is to aggregate some (not all) elements of a stream to produce a result; it can be done by stream.flatMap(FlatMapper).findFirst(). If this use case is common enough it deserves a standalone method, say aggregatePartially(FlatMapper). Now if FlatMapper is needed in other places too, it could use a more general name; after all, it is pretty much a normal function, except it inserts its result in a sink instead of returning it.

Zhong Yu

On Tue, Feb 12, 2013 at 12:41 PM, Brian Goetz <brian.goetz at oracle.com> wrote:

Here's where things have currently landed with FlatMapper -- this is a type in java.util.stream, with nested specializations.

Full bikeshed season is now open. Are we OK with the name explodeInto()? Is this general enough to join the ranks of Function and Supplier as top-level types in java.util.function? @FunctionalInterface public interface FlatMapper<T, U> { void explodeInto(T element, Consumer sink); @FunctionalInterface interface ToInt { void explodeInto(T element, IntConsumer sink); } @FunctionalInterface interface ToLong { void explodeInto(T element, LongConsumer sink); } @FunctionalInterface interface ToDouble { void explodeInto(T element, DoubleConsumer sink); } @FunctionalInterface interface OfIntToInt { void explodeInto(int element, IntConsumer sink); } @FunctionalInterface interface OfLongToLong { void explodeInto(long element, LongConsumer sink); } @FunctionalInterface interface OfDoubleToDouble { void explodeInto(double element, DoubleConsumer sink); } }

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