From 46d425603bc4aa6613a816283e895ae5bde7035b Mon Sep 17 00:00:00 2001
From: Grzegorz Piwowarek <gpiwowarek@gmail.com>
Date: Mon, 14 Oct 2024 20:19:24 +0200
Subject: [PATCH] Introduce dedicated DistinctByKeepLastGatherer (#37)

---
 .../gatherers/DistinctByKeepLastGatherer.java | 38 +++++++++++++++++++
 .../pivovarit/gatherers/MoreGatherers.java    | 15 +-------
 2 files changed, 39 insertions(+), 14 deletions(-)
 create mode 100644 src/main/java/com/pivovarit/gatherers/DistinctByKeepLastGatherer.java

diff --git a/src/main/java/com/pivovarit/gatherers/DistinctByKeepLastGatherer.java b/src/main/java/com/pivovarit/gatherers/DistinctByKeepLastGatherer.java
new file mode 100644
index 0000000..0f7f88b
--- /dev/null
+++ b/src/main/java/com/pivovarit/gatherers/DistinctByKeepLastGatherer.java
@@ -0,0 +1,38 @@
+package com.pivovarit.gatherers;
+
+import java.util.LinkedHashMap;
+import java.util.Objects;
+import java.util.function.BiConsumer;
+import java.util.function.Function;
+import java.util.function.Supplier;
+import java.util.stream.Gatherer;
+
+record DistinctByKeepLastGatherer<T, U>(
+  Function<? super T, ? extends U> keyExtractor) implements Gatherer<T, LinkedHashMap<U, T>, T> {
+
+    DistinctByKeepLastGatherer {
+        Objects.requireNonNull(keyExtractor, "keyExtractor can't be null");
+    }
+
+    @Override
+    public Supplier<LinkedHashMap<U, T>> initializer() {
+        return LinkedHashMap::new;
+    }
+
+    @Override
+    public Integrator<LinkedHashMap<U, T>, T, T> integrator() {
+        return (state, element, _) -> {
+            state.put(keyExtractor.apply(element), element);
+            return true;
+        };
+    }
+
+    @Override
+    public BiConsumer<LinkedHashMap<U, T>, Downstream<? super T>> finisher() {
+        return (state, downstream) -> {
+            for (T element : state.values()) {
+                downstream.push(element);
+            }
+        };
+    }
+}
diff --git a/src/main/java/com/pivovarit/gatherers/MoreGatherers.java b/src/main/java/com/pivovarit/gatherers/MoreGatherers.java
index 1ef38e2..801f654 100644
--- a/src/main/java/com/pivovarit/gatherers/MoreGatherers.java
+++ b/src/main/java/com/pivovarit/gatherers/MoreGatherers.java
@@ -2,7 +2,6 @@
 
 import java.util.HashSet;
 import java.util.Iterator;
-import java.util.LinkedHashMap;
 import java.util.Map;
 import java.util.Objects;
 import java.util.function.BiFunction;
@@ -24,19 +23,7 @@ private MoreGatherers() {
     }
 
     public static <T, U> Gatherer<T, ?, T> distinctByKeepLast(Function<? super T, ? extends U> keyExtractor) {
-        Objects.requireNonNull(keyExtractor, "keyExtractor can't be null");
-        return Gatherer.ofSequential(
-          LinkedHashMap<U, T>::new,
-          (state, element, _) -> {
-              state.put(keyExtractor.apply(element), element);
-              return true;
-          },
-          (state, downstream) -> {
-              for (T element : state.values()) {
-                  downstream.push(element);
-              }
-          }
-        );
+        return new DistinctByKeepLastGatherer<>(keyExtractor);
     }
 
     public static <T, U> Gatherer<T, ?, T> distinctBy(Function<? super T, ? extends U> keyExtractor) {