Github user tdas commented on a diff in the pull request: https://github.com/apache/spark/pull/9256#discussion_r44206972 --- Diff: streaming/src/main/scala/org/apache/spark/streaming/StateSpec.scala --- @@ -0,0 +1,181 @@ +/* + * 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.spark.streaming + +import scala.reflect.ClassTag + +import org.apache.spark.annotation.Experimental +import org.apache.spark.api.java.JavaPairRDD +import org.apache.spark.rdd.RDD +import org.apache.spark.{HashPartitioner, Partitioner} + + +/** + * :: Experimental :: + * Abstract class representing all the specifications of the DStream transformation + * `trackStateByKey` operation of a + * [[org.apache.spark.streaming.dstream.PairDStreamFunctions pair DStream]] (Scala) or a + * [[org.apache.spark.streaming.api.java.JavaPairDStream JavaPairDStream]] (Java). + * Use the [[org.apache.spark.streaming.StateSpec StateSpec.apply()]] or + * [[org.apache.spark.streaming.StateSpec StateSpec.create()]] to create instances of + * this class. + * + * Example in Scala: + * {{{ + * val spec = StateSpec(trackingFunction).numPartitions(10) + * + * val emittedRecordDStream = keyValueDStream.trackStateByKey[StateType, EmittedDataType](spec) + * }}} + * + * Example in Java: + * {{{ + * StateStateSpec[StateType, EmittedDataType] spec = + * StateStateSpec.create[StateType, EmittedDataType](trackingFunction).numPartition(10); + * + * JavaDStream[EmittedDataType] emittedRecordDStream = + * javaPairDStream.trackStateByKey[StateType, EmittedDataType](spec); + * }}} + */ +@Experimental +sealed abstract class StateSpec[K, V, S, T] extends Serializable { + + /** Set the RDD containing the initial states that will be used by `trackStateByKey`*/ --- End diff -- Actually, I correct myself. have `object StateSpec { def apply() ... }` and `class StateSpec { def function(...) }` makes the syntax cumbersome as that can be called only as `StateSpec().function(func)` ( not `StateSpec.function(func)` that I had thought earlier). To achieve `StateSpec.function(func)`, the method `function` must be a method of the object, like `StateSpec.apply()`. That does not solve @pwendell 's problem of not having the setter method `function` in the class. We could have both - the method `function` on both the class and object. That would solve both problems - use the object `StateSpec.function(func)` and `function` setter in the `StateSpec` class. But that would also allow the user to write `StateSpec.function(func1).function(func2)`. What should the semantics be in that case?
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