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https://issues.apache.org/jira/browse/FLINK-4883?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15611756#comment-15611756
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Renkai Ge commented on FLINK-4883:
----------------------------------

How about to extend the method 
org.apache.flink.streaming.api.datastream.DataStream#clean to make it not only 
clean the function but also check if the function is a scala object, I think 
it's the way to implement the detection with minimal changes.

> 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
>            Assignee: Renkai Ge
>
> 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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