content: /*
   * 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.beam.sdk.transforms;
  
  import java.io.Serializable;
  import java.util.Comparator;
  import java.util.Objects;
  import java.util.function.Function;
  
  /**
   * A {@code Comparator} that is also {@code Serializable}.
   *
   * @param <T> type of values being compared
   */
  public interface SerializableComparator<T> extends Comparator<T>, Serializable {
    /**
     * Analogous to {@link Comparator#comparing(Function)}, except that it takes in a {@link
     * SerializableFunction} as the key extractor and returns a {@link SerializableComparator}.
     *
     * @param keyExtractor the function used to extract the {@link java.lang.Comparable} sort key
     * @return A {@link SerializableComparator} that compares by an extracted key
     * @param <T> the type of element to be compared
     * @param <V> the type of the {@code Comparable} sort key
     * @see Comparator#comparing(Function)
     */
    static <T, V extends Comparable<? super V>> SerializableComparator<T> comparing(
        SerializableFunction<? super T, ? extends V> keyExtractor) {
      Objects.requireNonNull(keyExtractor);
      return (SerializableComparator<T>)
          (c1, c2) -> keyExtractor.apply(c1).compareTo(keyExtractor.apply(c2));
    }
  }
  