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https://issues.apache.org/jira/browse/FLINK-6552?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16008051#comment-16008051
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Aljoscha Krettek commented on FLINK-6552:
-----------------------------------------
Congratulations, you found a bug! 😅
I have a PR coming up in a sec. Thanks a lot for looking into this!
> Side outputs don't allow differing output types
> -----------------------------------------------
>
> Key: FLINK-6552
> URL: https://issues.apache.org/jira/browse/FLINK-6552
> Project: Flink
> Issue Type: Improvement
> Components: DataStream API
> Affects Versions: 1.3.0, 1.4.0
> Reporter: Chesnay Schepler
> Assignee: Aljoscha Krettek
>
> When calling {SingleOutputStreamOperator#getSideOutput(OutputTag<X>} multiple
> times with the output tags having different types you get the following
> exception:
> {code}
> "Trying to add a side input for the same id with a different type. This is
> not allowed."
> {code}
> This error message is ambiguous, as it could either mean that you cannot add
> 2 side outputs with the same name but different types or that 2 side outputs
> with different types cannot be retrieved from a single operator.
> Furthermore, the error message contains the concept of node id's (i guess?)
> which users aren't exposed to. This is confusing and should be reworded to
> work with operators.
> Lastly, i find this limitation rather odd. It is possible for an operator to
> have multiple side outputs. It is also possible to have a side output with a
> different type than the main output. Yet, it is not possible to have multiple
> side outputs with different types.
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