FlatMapper

[Brian Goetz]

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<U> sink);

     @FunctionalInterface
     interface ToInt<T> {
         void explodeInto(T element, IntConsumer sink);
     }

     @FunctionalInterface
     interface ToLong<T> {
         void explodeInto(T element, LongConsumer sink);
     }

     @FunctionalInterface
     interface ToDouble<T> {
         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);
     }
}