ReactorIntegerStream.kt

        val toIntegerStream = Function<String, Flux<Int>> { string ->
            Flux.fromIterable(IterableSpliterator.of(string.chars().boxed().spliterator()))
        }

        val histoOfLetters = Function<String, Flux<HashMap<Int, LongWrapper>>> { word ->
            Flux.from(toIntegerStream.apply(word)
                .collect(
                    { HashMap() },
                    { map: HashMap<Int, LongWrapper>, value: Int ->
                        var newValue: LongWrapper? = map[value]
                        if (newValue == null) {
                            newValue = LongWrapper.zero()
                        }
                        map[value] = newValue.incAndSet()
                    }

                ))
        }