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From: fhueske <git@git.apache.org>
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Subject: [GitHub] flink pull request #3354: [FLINK-5767] [Table] New aggregate function interf...
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Message-Id: <20170222130743.1EC1EDFF13@git1-us-west.apache.org>
Date: Wed, 22 Feb 2017 13:07:43 +0000 (UTC)
archived-at: Wed, 22 Feb 2017 13:07:53 -0000

Github user fhueske commented on a diff in the pull request:

    https://github.com/apache/flink/pull/3354#discussion_r102220814
  
    --- Diff: flink-libraries/flink-table/src/main/scala/org/apache/flink/table/functions/AggregateFunction.scala ---
    @@ -0,0 +1,73 @@
    +/*
    + * 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.table.functions
    +
    +/**
    +  * Base class for User-Defined Aggregates.
    +  *
    +  * @tparam T the type of the aggregation result
    +  */
    +abstract class AggregateFunction[T] extends UserDefinedFunction {
    +  /**
    +    * Create and init the Accumulator for this [[AggregateFunction]].
    +    *
    +    * @return the accumulator with the initial value
    +    */
    +  def createAccumulator(): Accumulator
    +
    +  /**
    +    * Called every time when an aggregation result should be materialized.
    +    * The returned value could be either a speculative result (periodically
    +    * emitted as data arrive) or the final result of the aggregation (when
    +    * the state of the aggregation is completely removed).
    --- End diff --
    
    How would the function distinguish these cases? 
    I think we should not mention that the state is removed because it is not the responsibility of the method.


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