/**
* 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;
/**
* This interface extends the <tt>GenericUDAFResolver</tt> interface and
* provides more flexibility in terms of discovering the parameter types
* supplied to the UDAF. Implementations that extend this interface will
* also have access to extra information such as the specification of the
* <tt>DISTINCT</tt> qualifier or the invocation with the special wildcard
* character.
* <p>
* <b>Note:</b> The implementation of function does not have to handle the
* actual <tt>DISTINCT</tt> or wildcard implementation. This information is
* provided only to allow the function implementation to accept or reject
* such invocations. For example - the implementation of <tt>COUNT</tt> UDAF
* requires that the <tt>DISTINCT</tt> qualifier be supplied when more than
* one parameters are specified in the invocation. The actual filtering of
* data bound to parameter types for <tt>DISTINCT</tt> implementation is
* handled by the framework and not the <tt>COUNT</tt> UDAF implementation.
*/
@SuppressWarnings("deprecation")
public interface GenericUDAFResolver2 extends 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 info The parameter information that is applicable to the UDAF being
* invoked.
* @throws SemanticException
*/
GenericUDAFEvaluator getEvaluator(
GenericUDAFParameterInfo info) throws SemanticException;
}