Hi Rémi,
>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).
Cheers,
√
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$
[2]
https://urldefense.com/v3/__https://github.com/forax/advent-of-code-2024__;!!ACWV5N9M2RV99hQ!J6APK3GQDbT-T1edAyWssnGHideZ-3rnwBQ39CsaHnc0y6OLh0fpSub1gPWjXsfzHl4OfAtxfQvA1n-w8kEG$
