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https://issues.apache.org/jira/browse/FLINK-4883?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15607635#comment-15607635
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Renkai Ge commented on FLINK-4883:
----------------------------------
I found a way to distinguish normal scala instances and objects, that is the
class name of scala objects would be suffixed by a `$` symbol.Though Java users
can name a class suffixed by a `$`, too, it is discouraged and seldom people
will do this.
I think we can scan every function in the generated execution plan before it
send to the cluster, if any function have a class name suffixed by `$`, we can
throw exception and tell them not to use scala object to extend functions.
The risk is, it seems distinguish object and normal class by class name is a
hacking but not scala standard, furture versions of scala may have a different
way to implement object then this method lost effectiveness.
What's your opinion? [~srichter]
> 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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