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From "Aljoscha Krettek (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-3869) WindowedStream.apply with FoldFunction is too restrictive
Date Fri, 16 Sep 2016 08:41:21 GMT

    [ https://issues.apache.org/jira/browse/FLINK-3869?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15495761#comment-15495761
] 

Aljoscha Krettek commented on FLINK-3869:
-----------------------------------------

I have another proposal for solving this: I started to dislike how the reduce/fold with window
function is called {{apply()}}. Yes, You can see the apply with incremental aggregation as
either an apply that has an additional incremental aggregation function or as an incremental
aggregation (reduce/fold) that has an apply added to it. Right now, I think these two methods
should be:
{code}
reduce(ReduceFunction, WindowFunction)
fold(Initial, FoldFunction, WindowFunction)
{code}

this would make them more discoverable, i.e. you do a reduce and then you see that you can
also give a {{WindowFunction}} to get all the meta data for the window.

If we changed to that new naming scheme we could fix the fold restriction and deprecate the
old methods, thereby not breaking any existing code.

[~StephanEwen] what do you think?

> WindowedStream.apply with FoldFunction is too restrictive
> ---------------------------------------------------------
>
>                 Key: FLINK-3869
>                 URL: https://issues.apache.org/jira/browse/FLINK-3869
>             Project: Flink
>          Issue Type: Sub-task
>          Components: Streaming
>            Reporter: Aljoscha Krettek
>            Assignee: Aljoscha Krettek
>
> Right now we have this signature:
> {code}
> public <R> SingleOutputStreamOperator<R> apply(R initialValue, FoldFunction<T,
R> foldFunction, WindowFunction<R, R, K, W> function) {
> {code}
> but we should have this signature to allow users to return a type other than the fold
accumulator type from their window function:
> {code}
> public <ACC, R> SingleOutputStreamOperator<R> apply(ACC initialValue, FoldFunction<T,
ACC> foldFunction, WindowFunction<ACC, R, K, W> function) {
> {code}



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