Method biFlatMap

future-java/src/main/java/io/trane/future/Promise.java:597–609

(final Future<U> other,
      final BiFunction<? super T, ? super U, ? extends Future<R>> f)

  }

  @Override
  public <U, R> Future<R> biFlatMap(final Future<U> other,
      final BiFunction<? super T, ? super U, ? extends Future<R>> f) {
    if (getInterruptHandler() != null)
      return continuation(new BiFlatMap<T, U, R>(other, f) {
        @Override
        protected final InterruptHandler getInterruptHandler() {
          return InterruptHandler.apply(Promise.this, other);
        }
      });
    else
      return continuation(new BiFlatMap<T, U, R>(other, f));
  }

  private static class Ensure<T> extends Continuation<T, T> {
    private final Runnable f;