Introduce dedicated ZipIteratorGatherer (#35)

src/main/java/com/pivovarit/gatherers/MoreGatherers.java

@@ -5,15 +5,11 @@
 import java.util.LinkedHashMap;
 import java.util.Map;
 import java.util.Objects;
-import java.util.concurrent.atomic.AtomicLong;
 import java.util.function.BiFunction;
 import java.util.function.Function;
 import java.util.stream.Gatherer;
 import java.util.stream.Stream;
 
-import static java.util.stream.Gatherer.Integrator.ofGreedy;
-import static java.util.stream.Gatherer.ofSequential;
-
 public final class MoreGatherers {
 
     private MoreGatherers() {
@@ -108,19 +104,7 @@ class State {
     }
 
     public static <T1, T2, R> Gatherer<T1, ?, R> zip(Iterator<T2> iterator, BiFunction<? super T1, ? super T2, ? extends R> mapper) {
-        Objects.requireNonNull(mapper, "mapper can't be null");
-        Objects.requireNonNull(iterator, "iterator can't be null");
-
-        return Gatherer.ofSequential(
-          () -> iterator,
-          (state, element, downstream) -> {
-              if (state.hasNext()) {
-                  downstream.push(mapper.apply(element, state.next()));
-                  return true;
-              } else {
-                  return false;
-              }
-          });
+        return new ZipIteratorGatherer<>(iterator, mapper);
     }
 
     public static <T, R> Gatherer<T, ?, R> zipWithIndex(BiFunction<Long, ? super T, ? extends R> mapper) {

src/main/java/com/pivovarit/gatherers/ZipIteratorGatherer.java

@@ -0,0 +1,33 @@
+package com.pivovarit.gatherers;
+
+import java.util.Iterator;
+import java.util.Objects;
+import java.util.function.BiFunction;
+import java.util.function.Supplier;
+import java.util.stream.Gatherer;
+
+record ZipIteratorGatherer<T1, T2, R>(Iterator<T2> iterator, BiFunction<? super T1, ? super T2, ? extends R> mapper)
+  implements Gatherer<T1, Iterator<T2>, R> {
+
+    ZipIteratorGatherer {
+        Objects.requireNonNull(mapper, "mapper can't be null");
+        Objects.requireNonNull(iterator, "iterator can't be null");
+    }
+
+    @Override
+    public Supplier<Iterator<T2>> initializer() {
+        return () -> iterator;
+    }
+
+    @Override
+    public Integrator<Iterator<T2>, T1, R> integrator() {
+        return (state, element, downstream) -> {
+            if (state.hasNext()) {
+                downstream.push(mapper.apply(element, state.next()));
+                return true;
+            } else {
+                return false;
+            }
+        };
+    }
+}