001/**
002 * The MIT License (MIT)
003 *
004 * Copyright (c) 2019 nobark (tools4j), Marco Terzer, Anton Anufriev
005 *
006 * Permission is hereby granted, free of charge, to any person obtaining a copy
007 * of this software and associated documentation files (the "Software"), to deal
008 * in the Software without restriction, including without limitation the rights
009 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
010 * copies of the Software, and to permit persons to whom the Software is
011 * furnished to do so, subject to the following conditions:
012 *
013 * The above copyright notice and this permission notice shall be included in all
014 * copies or substantial portions of the Software.
015 *
016 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
017 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
018 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
019 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
020 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
021 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
022 * SOFTWARE.
023 */
024package org.tools4j.nobark.queue;
025
026/**
027 * Merger strategy passed to some conflation queues upon construction to support merging of values when conflation
028 * occurs.
029 *
030 * @param <K> the type of the conflation key
031 * @param <V> the type of values in the queue
032 */
033@FunctionalInterface
034public interface Merger<K,V> {
035    /**
036     * Method called to merge two values;  the merged value is returned.
037     *
038     * @param conflationKey the conflation key
039     * @param olderValue    the older value that was already present in the queue
040     * @param newValue      the newer value that is currently being added to the queue
041     * @return  the merged value; can be {@code newValue} itself but should not be {@code olderValue} as this instance
042     *          is returned by the enqueue method and may be reused by the producer
043     */
044    V merge(K conflationKey, V olderValue, V newValue);
045}