> From: "Viktor Klang" <viktor.kl...@oracle.com>
> To: "Remi Forax" <fo...@univ-mlv.fr>, "core-libs-dev"
> <core-libs-...@openjdk.java.net>
> Sent: Thursday, January 2, 2025 12:26:08 PM
> Subject: Re: [External] : Gatherers.fold()
> Hi Rémi,
Happy new year,
>>Thinking a little more, i do not understand why fold takes a Supplier as first
>>parameter and not just a value given that the Gatherer is created with
> >ofSequential().
> If it didn't take a supplier then the resulting Gatherer could never be reused
> (including composition). I.e. The use of Supplier for the state type is not
> primarily/only about parallelizability, but rather reuse (which subsumes
> parallelizability).
yes, it makes sense.
Okay, so there is just a missing wildcard when the Supplier is declared in
fold, thanks to the erasure (it's not something you often write :) ), it's a
backward compatible change.
> Cheers,
> √
regards,
Rémi
> Viktor Klang
> Software Architect, Java Platform Group
> Oracle
> From: Remi Forax <fo...@univ-mlv.fr>
> Sent: Friday, 20 December 2024 10:39
> To: core-libs-dev <core-libs-...@openjdk.java.net>
> Cc: Viktor Klang <viktor.kl...@oracle.com>
> Subject: [External] : Gatherers.fold()
> Hello Victor,
> for the Advent of code of yesterday [1], i've this code golfing solution (the
> full code is here [2])
> var input = ...;
> class Node {
> final HashMap<Integer, Node> map = new HashMap<>();
> boolean end;
> }
> var root = new Node();
> Arrays.stream(input.substring(0, input.indexOf('\n')).split(", "))
> .forEach(w -> w.chars().boxed().gather(Gatherers.fold(() -> root,
> (n, c) -> n.map.computeIfAbsent(c, _ -> new
> Node()))).findFirst().orElseThrow().end = true);
> println(input.lines().skip(2).filter(w ->
> w.chars().boxed().<Set<Node>>gather(Gatherers.fold(() -> new
> HashSet<>(Set.of(root)),
> (ms, c) -> ms.stream().flatMap(m -> Stream.ofNullable(m.map.get(c)))
> .flatMap(n -> n != null && n.end ? Stream.of(n, root) :
> Stream.ofNullable(n)).collect(Collectors.toSet())))
> .findFirst().orElseThrow().stream().anyMatch(n -> n.end)).count());
> As you can see, the second call to Gatherers.fold() requires to specify the
> type
> argument, the <Set<Node>> in front because the supplier is not declared as a
> Supplier<? extends ...>
> Thinking a little more, i do not understand why fold takes a Supplier as first
> parameter and not just a value given that the Gatherer is created with
> ofSequential().
> regards,
> Rémi
> [1] [
> https://urldefense.com/v3/__https://adventofcode.com/2024/day/19__;!!ACWV5N9M2RV99hQ!J6APK3GQDbT-T1edAyWssnGHideZ-3rnwBQ39CsaHnc0y6OLh0fpSub1gPWjXsfzHl4OfAtxfQvA1k3dUfis$
> |
> https://urldefense.com/v3/__https://adventofcode.com/2024/day/19__;!!ACWV5N9M2RV99hQ!J6APK3GQDbT-T1edAyWssnGHideZ-3rnwBQ39CsaHnc0y6OLh0fpSub1gPWjXsfzHl4OfAtxfQvA1k3dUfis$
> ]
> [2] [
> https://urldefense.com/v3/__https://github.com/forax/advent-of-code-2024__;!!ACWV5N9M2RV99hQ!J6APK3GQDbT-T1edAyWssnGHideZ-3rnwBQ39CsaHnc0y6OLh0fpSub1gPWjXsfzHl4OfAtxfQvA1n-w8kEG$
> |
> https://urldefense.com/v3/__https://github.com/forax/advent-of-code-2024__;!!ACWV5N9M2RV99hQ!J6APK3GQDbT-T1edAyWssnGHideZ-3rnwBQ39CsaHnc0y6OLh0fpSub1gPWjXsfzHl4OfAtxfQvA1n-w8kEG$
> ]
