[jira] [Created] (FLINK-4883) Prevent UDFs implementations through Scala singleton objects

[Shang Yuanchun (Jira)]

Stefan Richter created FLINK-4883:
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             Summary: Prevent UDFs implementations through Scala singleton objects
                 Key: FLINK-4883
                 URL: https://issues.apache.org/jira/browse/FLINK-4883
             Project: Flink
          Issue Type: Bug
            Reporter: Stefan Richter


Currently, user can create and use UDFs in Scala like this:

{code}
object FlatMapper extends RichCoFlatMapFunction[Long, String, (Long, String)] {
...
}
{code}

However, this leads to problems as the UDF is now a singleton that Flink could use across several operator instances, which leads to job failures. We should detect and prevent the usage of singleton UDFs.



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