throw new RejectedExecutionException();
        }
      };

  private static <V> AsyncFunction<V, V> asyncIdentity() {
    return Futures::immediateFuture;
  }

  private static <I, O> AsyncFunction<I, O> tagged(String toString, AsyncFunction<I, O> function) {
    return new AsyncFunction<I, O>() {
      @Override
      public ListenableFuture<O> apply(I input) throws Exception {

          throw new RejectedExecutionException();
        }
      };

  private static <V> AsyncFunction<V, V> asyncIdentity() {
    return Futures::immediateFuture;
  }

  private static <I, O> AsyncFunction<I, O> tagged(String toString, AsyncFunction<I, O> function) {
    return new AsyncFunction<I, O>() {
      @Override
      public ListenableFuture<O> apply(I input) throws Exception {

      Class<X> exceptionType, AsyncClosingFunction<? super X, W> fallback, Executor executor) {
    checkNotNull(fallback);
    AsyncFunction<X, W> asyncFunction =
        new AsyncFunction<X, W>() {
          @Override
          public ListenableFuture<W> apply(X exception) throws Exception {
            return state.closeables.applyAsyncClosingFunction(fallback, exception);