[jira] [Commented] (FLINK-5914) remove aggregateResultType from streaming.api.datastream.aggregate

["Aljoscha Krettek (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/FLINK-5914?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15884272#comment-15884272 ] 

Aljoscha Krettek commented on FLINK-5914:
-----------------------------------------

The reason for the {{WindowFunction}} input type (which is also the {{AggregateFunction}} result type) being different from the {{WindowFunction}} result type is to allow the user to enrich the result from the {{AggregateFunction}} with meta information about the window firing that is only available to the {{WindowFunction}} or {{ProcessWindowFunction}}. Right now, the only meta information available is the {{Window}} for which this firing is happening but in the future this will be extended with, for example, a lateness specification, the number of window firings, etc.

What's the reason for wanting to remove the result/intermediate type? I think it would only restrict what a user can do and this restriction was considered a bug for {{fold()}}: FLINK-3869.

> remove aggregateResultType from streaming.api.datastream.aggregate
> ------------------------------------------------------------------
>
>                 Key: FLINK-5914
>                 URL: https://issues.apache.org/jira/browse/FLINK-5914
>             Project: Flink
>          Issue Type: Improvement
>          Components: DataStream API
>            Reporter: Shaoxuan Wang
>            Assignee: Shaoxuan Wang
>
> aggregateResultType does not seem necessary for streaming.api.datastream.aggregate. We will anyway not serialize the aggregateResult between aggregate and window function. Aggregate function itself provides a function to getResult(), window function here should just emit the same results as aggregate output. So aggregateResultType should be same as resultType. I think we can safely remove aggregateResultType, thereby user will not have to provide two same types for the streaming.api.datastream.aggregate.  
>  [~StephanEwen], what do you think?



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