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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-2809) DataSet[Unit] doesn't work
Date Sat, 17 Oct 2015 10:19:05 GMT

    [ https://issues.apache.org/jira/browse/FLINK-2809?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14961835#comment-14961835
] 

ASF GitHub Bot commented on FLINK-2809:
---------------------------------------

Github user aalexandrov commented on the pull request:

    https://github.com/apache/flink/pull/1217#issuecomment-148901986
  
    > Not all methods without paremeters should translate to methods without parenthesis...
    
    @StephanEwen I agree with that, but I cannot understand how the `UnitTypeInfo` might cause
a confusion here.
    
    The typeInformation macros are synthesized by the macro based on the inferred collection
type, which means that the meaning of `()` is resolved before that. Consider the following
example:
    
    ```scala
    // in the Scala REPL
    
    case class Foo(answer: Int)
    // defined class Foo
    
    def f1(): Foo = Foo(42)
    // f1: ()Foo
    
    def f2: Foo = Foo(42)
    // f2: Foo
    
    val xs = Seq(f1(), f2) // how a literate person would write it
    // xs: Seq[Foo] = List(Foo(42), Foo(42))
    
    val xs = Seq(f1, f2) // how a dazed & confused person would write it, but still compiles
 
    // xs: Seq[Foo] = List(Foo(42), Foo(42))
    
    val xs = Seq(f1, f2()) // even worse, but this breaks with a compiler exception
    // error: Foo does not take parameters
    //       val xs = Seq(f1, f2())
    
    val xs = Seq((), ()) // typing '()' without syntactic context resolves to Unit
    // xs: Seq[Unit] = List((), ())
    ```
    
    In all of the above situations `env.fromCollection(xs)` is (1) either going to typecheck
and trigger `TypeInformation` synthesis or (2) fail with the above.
    
    Can you point to StackOverflow conversation or something similar where the issue you mention
is explained with an example?


> DataSet[Unit] doesn't work
> --------------------------
>
>                 Key: FLINK-2809
>                 URL: https://issues.apache.org/jira/browse/FLINK-2809
>             Project: Flink
>          Issue Type: Bug
>          Components: Scala API
>            Reporter: Gabor Gevay
>            Assignee: Gabor Gevay
>            Priority: Minor
>
> The following code creates a DataSet\[Unit\]:
>     val env = ExecutionEnvironment.createLocalEnvironment()
>     val a = env.fromElements(1,2,3)
>     val b = a.map (_ => ())
>     b.writeAsText("/tmp/xxx")
>     env.execute()
> This doesn't work, because a VoidSerializer is created, which can't cope with a BoxedUnit.
See exception below.
> I'm now thinking about creating a UnitSerializer class.
> org.apache.flink.runtime.client.JobExecutionException: Job execution failed.
> 	at org.apache.flink.runtime.jobmanager.JobManager$$anonfun$receiveWithLogMessages$1.applyOrElse(JobManager.scala:314)
> 	at scala.runtime.AbstractPartialFunction.apply(AbstractPartialFunction.scala:36)
> 	at org.apache.flink.runtime.ActorLogMessages$$anon$1.apply(ActorLogMessages.scala:36)
> 	at org.apache.flink.runtime.ActorLogMessages$$anon$1.apply(ActorLogMessages.scala:29)
> 	at scala.PartialFunction$class.applyOrElse(PartialFunction.scala:123)
> 	at org.apache.flink.runtime.ActorLogMessages$$anon$1.applyOrElse(ActorLogMessages.scala:29)
> 	at akka.actor.Actor$class.aroundReceive(Actor.scala:465)
> 	at org.apache.flink.runtime.jobmanager.JobManager.aroundReceive(JobManager.scala:92)
> 	at akka.actor.ActorCell.receiveMessage(ActorCell.scala:516)
> 	at akka.actor.ActorCell.invoke(ActorCell.scala:487)
> 	at akka.dispatch.Mailbox.processMailbox(Mailbox.scala:254)
> 	at akka.dispatch.Mailbox.run(Mailbox.scala:221)
> 	at akka.dispatch.Mailbox.exec(Mailbox.scala:231)
> 	at scala.concurrent.forkjoin.ForkJoinTask.doExec(ForkJoinTask.java:260)
> 	at scala.concurrent.forkjoin.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1339)
> 	at scala.concurrent.forkjoin.ForkJoinPool.runWorker(ForkJoinPool.java:1979)
> 	at scala.concurrent.forkjoin.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:107)
> Caused by: java.lang.ClassCastException: scala.runtime.BoxedUnit cannot be cast to java.lang.Void
> 	at org.apache.flink.api.common.typeutils.base.VoidSerializer.serialize(VoidSerializer.java:26)
> 	at org.apache.flink.runtime.plugable.SerializationDelegate.write(SerializationDelegate.java:51)
> 	at org.apache.flink.runtime.io.network.api.serialization.SpanningRecordSerializer.addRecord(SpanningRecordSerializer.java:76)
> 	at org.apache.flink.runtime.io.network.api.writer.RecordWriter.emit(RecordWriter.java:83)
> 	at org.apache.flink.runtime.operators.shipping.OutputCollector.collect(OutputCollector.java:65)
> 	at org.apache.flink.runtime.operators.chaining.ChainedMapDriver.collect(ChainedMapDriver.java:78)
> 	at org.apache.flink.runtime.operators.DataSourceTask.invoke(DataSourceTask.java:177)
> 	at org.apache.flink.runtime.taskmanager.Task.run(Task.java:564)
> 	at java.lang.Thread.run(Thread.java:745)



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