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ValueMerger.java
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ValueMerger.java
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/*
* Copyright (c) 2002-2017 "Neo Technology,"
* Network Engine for Objects in Lund AB [http://neotechnology.com]
*
* This file is part of Neo4j.
*
* Neo4j is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
package org.neo4j.index.internal.gbptree;
/**
* Decides what to do when inserting key which already exists in index. Different implementations of
* {@link ValueMerger} can result in unique/non-unique indexes for example.
*
* @param <VALUE> type of values to merge.
*/
public interface ValueMerger<KEY,VALUE>
{
/**
* Merge an existing value with a new value, returning potentially a combination of the two, or {@code null}
* if no merge was done effectively meaning that nothing should be written.
*
* @param existingKey existing key
* @param newKey new key
* @param existingValue existing value
* @param newValue new value
* @return {@code newValue}, now merged with {@code existingValue}, or {@code null} if no merge was done.
*/
VALUE merge( KEY existingKey, KEY newKey, VALUE existingValue, VALUE newValue );
}