[jira] [Commented] (FLINK-12121) Use composition instead of inheritance for the InternalKeyContext logic in backend

["Yu Li (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/FLINK-12121?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16812243#comment-16812243 ] 

Yu Li commented on FLINK-12121:
-------------------------------

Mark as a blocker of FLINK-12066

> Use composition instead of inheritance for the InternalKeyContext logic in backend
> ----------------------------------------------------------------------------------
>
>                 Key: FLINK-12121
>                 URL: https://issues.apache.org/jira/browse/FLINK-12121
>             Project: Flink
>          Issue Type: Improvement
>          Components: Runtime / State Backends
>            Reporter: Yu Li
>            Assignee: Yu Li
>            Priority: Major
>
> Commonly it's [recommended|https://stackoverflow.com/questions/2399544/difference-between-inheritance-and-composition] to favor composition over inheritance in java design, but currently in keyed backend we're using inheritance for the {{InternalKeyContext}} logic, and here we propose to change to the composition way.
> Another advantage of changing to the composition way is that we could remove the requirement of a heap backend instance when constructing {{HeapRestoreOperation}}, and further making sure all fields are final when constructing the {{HeapKeyedStateBackend}}



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