content: /*
   * Copyright (C) 2020 ActiveJ LLC.
   *
   * Licensed 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 io.activej.cube.aggregation;
  
  /**
   * Accumulates records using arithmetic summation.
   */
  public interface Aggregate<T, A> {
  	/**
  	 * Creates an object which holds arithmetic sum of accumulated records.
  	 *
  	 * @param record record whose fields are to be accumulated
  	 * @return accumulator object
  	 */
  	A createAccumulator(T record);
  
  	/**
  	 * Performs the following operation: accumulator = accumulator + record.
  	 *
  	 * @param accumulator accumulator which holds the current sum of records
  	 * @param record      record to add to the accumulator
  	 */
  	void accumulate(A accumulator, T record);
  }
  