org.apache.flink.runtime.state.StateTransformationFunction Maven / Gradle / Ivy

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/*
 * 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,
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 * See the License for the specific language governing permissions and
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 */

package org.apache.flink.runtime.state;

import org.apache.flink.annotation.Internal;

/**
 * Interface for a binary function that is used for push-down of state transformation into state
 * backends. The function takes as inputs the old state and an element. From those inputs, the
 * function computes the new state.
 *
 * @param  type of the previous state that is the bases for the computation of the new state.
 * @param  type of the element value that is used to compute the change of state.
 */
@Internal
public interface StateTransformationFunction {

    /**
     * Binary function that applies a given value to the given old state to compute the new state.
     *
     * @param previousState the previous state that is the basis for the transformation.
     * @param value the value that the implementation applies to the old state to obtain the new
     *     state.
     * @return the new state, computed by applying the given value on the given old state.
     * @throws Exception if something goes wrong in applying the transformation function.
     */
    S apply(S previousState, T value) throws Exception;
}