[jira] [Assigned] (KAFKA-4726) ValueMapper should have (read) access to key

["Matthias J. Sax (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/KAFKA-4726?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Matthias J. Sax reassigned KAFKA-4726:
--------------------------------------

    Assignee: Jeyhun Karimov

> ValueMapper should have (read) access to key
> --------------------------------------------
>
>                 Key: KAFKA-4726
>                 URL: https://issues.apache.org/jira/browse/KAFKA-4726
>             Project: Kafka
>          Issue Type: Improvement
>          Components: streams
>    Affects Versions: 0.10.1.1
>            Reporter: Steven Schlansker
>            Assignee: Jeyhun Karimov
>              Labels: kip
>
> {{ValueMapper}} should have read-only access to the key for the value it is mapping.  Sometimes the value transformation will depend on the key.
> It is possible to do this with a full blown {{KeyValueMapper}} but that loses the promise that you won't change the key -- so you might introduce a re-keying phase that is totally unnecessary.  It also requires you to return an identity KeyValue object which costs something to construct (unless we are lucky and the optimizer elides it).
> [ If mapValues() is guaranteed to be no less efficient than map() the issue may be moot, but I presume there are some optimizations that are valid with the former but not latter. ]



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