A Small Exercise with Java's CompletableFuture

One of the cool features about Reactive Java is the Mono::zip or Flux::zip which allows you to combine unrelated Mono/Flux results:

I was doing some Java optimization the other day and was forced into using CompletableFuture constructs (it was using Java 8), it was the one thing that I needed.

CompletableFuture<Integer> future1 = CompletableFuture.supplyAsync(() -> 1);
CompletableFuture<String> future2 = CompletableFuture.supplyAsync(() -> "Hello");
CompletableFuture<Double> future3 = CompletableFuture.supplyAsync(() -> 3.14);        

Every solution i found out there (which includes ChatGPT) is recommending CompletableFuture::allOf which IMO is not very clean/elegant (less idiomatic)

var combinedFuture = CompletableFuture.allOf(future1, future2, future3)
  .thenApply(v -> {
            try {
                Integer result1 = future1.get();
                String result2 = future2.get();
                Double result3 = future3.get();
                return new Tuple.of(result1, result2, result3);
            } catch (Exception e) {
                throw new RuntimeException(e);
            }
        });        

(Note that I’m using vavr’s Tuple type since Java 8 doesn’t have it)

After much thinking I came up with this solution:

var combinedResults = future1
  .thenCombine(future2, Tuple::of)
  .thenApply(future3, (t, e) -> t.concat(Tuple.of(e)));        

The clear take-away here is nobody should be thinking about these things on a Thanksgiving long weekend. ??