/*
* 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.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 <S> type of the previous state that is the bases for the computation of the new state.
* @param <T> type of the element value that is used to compute the change of state.
*/
@Internal
public interface StateTransformationFunction<S, T> {
/**
* 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;
}