Introduce dedicated DistinctByGatherer (#39)

pivovarit · Oct 14, 2024 · ef675c1 · ef675c1
1 parent b583152
commit ef675c1
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Showing 2 changed files with 30 additions and 11 deletions.
diff --git a/src/main/java/com/pivovarit/gatherers/DistinctByGatherer.java b/src/main/java/com/pivovarit/gatherers/DistinctByGatherer.java
@@ -0,0 +1,29 @@
+package com.pivovarit.gatherers;
+
+import java.util.HashSet;
+import java.util.Objects;
+import java.util.function.Function;
+import java.util.function.Supplier;
+import java.util.stream.Gatherer;
+
+record DistinctByGatherer<T, U>(Function<? super T, ? extends U> keyExtractor) implements Gatherer<T, HashSet<U>, T> {
+
+    DistinctByGatherer {
+        Objects.requireNonNull(keyExtractor, "keyExtractor can't be null");
+    }
+
+    @Override
+    public Supplier<HashSet<U>> initializer() {
+        return HashSet::new;
+    }
+
+    @Override
+    public Integrator<HashSet<U>, T, T> integrator() {
+        return (state, element, downstream) -> {
+            if (state.add(keyExtractor.apply(element))) {
+                downstream.push(element);
+            }
+            return true;
+        };
+    }
+}
diff --git a/src/main/java/com/pivovarit/gatherers/MoreGatherers.java b/src/main/java/com/pivovarit/gatherers/MoreGatherers.java
@@ -1,6 +1,5 @@
 package com.pivovarit.gatherers;
 
-import java.util.HashSet;
 import java.util.Iterator;
 import java.util.Map;
 import java.util.Objects;
@@ -27,16 +26,7 @@ private MoreGatherers() {
     }
 
     public static <T, U> Gatherer<T, ?, T> distinctBy(Function<? super T, ? extends U> keyExtractor) {
-        Objects.requireNonNull(keyExtractor, "keyExtractor can't be null");
-        return Gatherer.ofSequential(
-          () -> new HashSet<U>(),
-          (state, element, downstream) -> {
-              if (state.add(keyExtractor.apply(element))) {
-                  downstream.push(element);
-              }
-              return true;
-          }
-        );
+        return new DistinctByGatherer<>(keyExtractor);
     }
 
     public static <T> Gatherer<T, ?, T> distinctUntilChanged() {