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https://issues.apache.org/jira/browse/FLINK-5024?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15872234#comment-15872234
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ASF GitHub Bot commented on FLINK-5024:
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Github user StephanEwen closed the pull request at:

    https://github.com/apache/flink/pull/3243


> Add SimpleStateDescriptor to clarify the concepts
> -------------------------------------------------
>
>                 Key: FLINK-5024
>                 URL: https://issues.apache.org/jira/browse/FLINK-5024
>             Project: Flink
>          Issue Type: Improvement
>          Components: State Backends, Checkpointing
>            Reporter: Xiaogang Shi
>            Assignee: Xiaogang Shi
>
> Currently, StateDescriptors accept two type arguments : the first one is the 
> type of the created state and the second one is the type of the values in the 
> states. 
> The concepts however is a little confusing here because in ListStates, the 
> arguments passed to the StateDescriptors are the types of the list elements 
> instead of the lists. It also makes the implementation of MapStates difficult.
> I suggest not to put the type serializer in StateDescriptors, making 
> StateDescriptors independent of the data structures of the values. 
> A new type of StateDescriptor named SimpleStateDescriptor can be provided to 
> abstract those states (namely ValueState, ReducingState and FoldingState) 
> whose states are not composited. 
> The states (e.g. ListStates and MapStates) can implement their own 
> descriptors according to their data structures. 



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