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https://issues.apache.org/jira/browse/FLINK-5024?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15643773#comment-15643773
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Aljoscha Krettek commented on FLINK-5024:
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The idea sounds reasonable. If you look at when I initially added
{{StateDescriptors}} it was actually like that:
https://github.com/apache/flink/commit/caf4672#diff-fa60b4ffb3c6ac5e6444f1d8efb66f30.
Only {{ValueState}} descriptor had the added functionality of storing a
default value.
> Add SimpleStateDescriptor to clarify the concepts
> -------------------------------------------------
>
> Key: FLINK-5024
> URL: https://issues.apache.org/jira/browse/FLINK-5024
> Project: Flink
> Issue Type: Improvement
> Reporter: 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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