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[jira] [Created] (FLINK-10167) SessionWindows not compatible with typed DataStreams in scala

Andrew Roberts created FLINK-10167:

             Summary: SessionWindows not compatible with typed DataStreams in scala
                 Key: FLINK-10167
                 URL: https://issues.apache.org/jira/browse/FLINK-10167
             Project: Flink
          Issue Type: Bug
            Reporter: Andrew Roberts

I'm trying to construct a trivial job that uses session windows, and it looks like the data type parameter is hardcoded to `Object`/`AnyRef`. Due to the invariance of java classes in scala, this means that we can't use the provided SessionWindow helper classes in scala on typed streams.


Example job:
import org.apache.flink.api.scala._
import org.apache.flink.streaming.api.scala.{DataStream, StreamExecutionEnvironment}
import org.apache.flink.streaming.api.windowing.assigners.ProcessingTimeSessionWindows
import org.apache.flink.streaming.api.windowing.time.Time
import org.apache.flink.streaming.api.windowing.windows.{TimeWindow, Window}
import org.apache.flink.util.Collector

object TestJob {
  val jobName = "TestJob"

  def main(args: Array[String]): Unit = {
    val env = StreamExecutionEnvironment.getExecutionEnvironment

    env.fromCollection(Range(0, 100).toList)
      .keyBy(_ / 10)
        (a: Int, b: Int) => a + b,
        (key: Int, window: Window, items: Iterable[Int], out: Collector[String]) => s"${key}: ${items}"


Compile error:
[error]  found   : org.apache.flink.streaming.api.windowing.assigners.ProcessingTimeSessionWindows
[error]  required: org.apache.flink.streaming.api.windowing.assigners.WindowAssigner[_ >: Int, ?]
[error] Note: Object <: Any (and org.apache.flink.streaming.api.windowing.assigners.ProcessingTimeSessionWindows <: org.apache.flink.streaming.api.windowing.assigners.MergingWindowAssigner[Object,org.apache.flink.streaming.api.windowing.windows.TimeWindow]), but Java-defined class WindowAssigner is invariant in type T.
[error] You may wish to investigate a wildcard type such as `_ <: Any`. (SLS 3.2.10)
[error]       .window(ProcessingTimeSessionWindows.withGap(Time.minutes(1))){code}

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