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https://issues.apache.org/jira/browse/HBASE-9359?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13752906#comment-13752906
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Jonathan Hsieh commented on HBASE-9359:
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Yup, I'm pretty convinced that preGet and postGet must be List<Cell> and not
List<? extends Cell>. If we have it as a List<? extends Cell> we get into
co/contra variance problems -- we can read the elements out of the list, but
when we cannot put things in in a typesafe way.
Suppose we don't know if the list is List<KeyValue> or List<Cell> (the case
with <? extends Cell>), Lets say it was actually a List<KeyValue> and we were
able to put in some non KeyValue derived Cell. The calling code, knowing the
list is a List<KeyValue> would attempt to read values out of the list and and
interpret them as KeyValue. This would be a type error causing runtime barf
since it was some other Cell.
By having it as a List<Cell> we can read and write in elements that are
subclasses of Cell as long as we only use the Cell interface.
> Convert KeyValue to Cell in hbase-client module - Result/Put/Delete,
> ColumnInterpreter
> --------------------------------------------------------------------------------------
>
> Key: HBASE-9359
> URL: https://issues.apache.org/jira/browse/HBASE-9359
> Project: HBase
> Issue Type: Sub-task
> Components: Client
> Affects Versions: 0.95.2
> Reporter: Jonathan Hsieh
> Assignee: Jonathan Hsieh
> Attachments: hbase-9359.patch
>
>
> This path is the second half of eliminating KeyValue from the client
> interfaces. This percolated through quite a bit.
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