Github user vanzin commented on a diff in the pull request:
https://github.com/apache/spark/pull/18221#discussion_r120677421
--- Diff:
common/kvstore/src/main/java/org/apache/spark/kvstore/ArrayWrappers.java ---
@@ -0,0 +1,214 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.kvstore;
+
+import java.util.Arrays;
+
+import com.google.common.base.Preconditions;
+import com.google.common.base.Objects;
+
+/**
+ * A factory for array wrappers so that arrays can be used as a key in a
map, sorted or not.
+ *
+ * The comparator implementation makes two assumptions:
+ * - All elements are instances of Comparable
+ * - When comparing two arrays, they both contain elements of the same
type in corresponding
+ * indices.
+ *
+ * Otherwise, ClassCastExceptions may occur. The equality method can
compare any two arrays.
+ *
+ * This class is not efficient and is mostly meant to compare really small
arrays, like those
+ * generally used as indices and keys in a KVStore.
+ */
+class ArrayWrappers {
+
+ @SuppressWarnings("unchecked")
+ public static Comparable<Object> forArray(Object a) {
+ Preconditions.checkArgument(a.getClass().isArray());
+ Comparable<?> ret;
+ if (a instanceof int[]) {
+ ret = new ComparableIntArray((int[]) a);
+ } else if (a instanceof long[]) {
+ ret = new ComparableLongArray((long[]) a);
+ } else if (a instanceof byte[]) {
+ ret = new ComparableByteArray((byte[]) a);
+ } else {
+
Preconditions.checkArgument(!a.getClass().getComponentType().isPrimitive());
+ ret = new ComparableObjectArray((Object[]) a);
+ }
+ return (Comparable<Object>) ret;
+ }
+
+ private static class ComparableIntArray implements
Comparable<ComparableIntArray> {
+
+ private final int[] array;
+
+ ComparableIntArray(int[] array) {
+ this.array = array;
+ }
+
+ @Override
+ public boolean equals(Object other) {
+ if (!(other instanceof ComparableIntArray)) {
+ return false;
+ }
+ return Arrays.equals(array, ((ComparableIntArray) other).array);
+ }
+
+ @Override
+ public int hashCode() {
+ int code = 0;
+ for (int i = 0; i < array.length; i++) {
+ code += array[i];
--- End diff --
Sure, that's easy enough.
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