/*
* 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.api.common.state;
import org.apache.flink.annotation.PublicEvolving;
import org.apache.flink.api.common.functions.AggregateFunction;
/**
* {@link State} interface for aggregating state, based on an
* {@link AggregateFunction}. Elements that are added to this type of state will
* be eagerly pre-aggregated using a given {@code AggregateFunction}.
*
* <p>The state holds internally always the accumulator type of the {@code AggregateFunction}.
* When accessing the result of the state, the function's
* {@link AggregateFunction#getResult(Object)} method.
*
* <p>The state is accessed and modified by user functions, and checkpointed consistently
* by the system as part of the distributed snapshots.
*
* <p>The state is only accessible by functions applied on a KeyedDataStream. The key is
* automatically supplied by the system, so the function always sees the value mapped to the
* key of the current element. That way, the system can handle stream and state partitioning
* consistently together.
*
* @param <IN> Type of the value added to the state.
* @param <OUT> Type of the value extracted from the state.
*/
@PublicEvolving
public interface AggregatingState<IN, OUT> extends MergingState<IN, OUT> {}