/**
 * 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.hadoop.hive.ql.udf.generic;

import org.apache.hadoop.hive.ql.parse.SemanticException;
import org.apache.hadoop.hive.serde2.typeinfo.TypeInfo;

/**
 * A Generic User-defined aggregation function (GenericUDAF) for the use with
 * Hive.
 *
 * GenericUDAFResolver is used at compile time. We use GenericUDAFResolver to
 * find out the GenericUDAFEvaluator for the parameter types.
 *
 * @deprecated Use {@link GenericUDAFResolver2} instead.
 */
@Deprecated
public interface GenericUDAFResolver {

  /**
   * Get the evaluator for the parameter types.
   *
   * The reason that this function returns an object instead of a class is
   * because it is possible that the object needs some configuration (that can
   * be serialized). In that case the class of the object has to implement the
   * Serializable interface. At execution time, we will deserialize the object
   * from the plan and use it to evaluate the aggregations.
   * <p>
   * If the class of the object does not implement Serializable, then we will
   * create a new instance of the class at execution time.
   * </p>
   * @param parameters
   *          The types of the parameters. We need the type information to know
   *          which evaluator class to use.
   * @throws SemanticException
   */
  GenericUDAFEvaluator getEvaluator(TypeInfo[] parameters)
    throws SemanticException;
}
