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https://issues.apache.org/jira/browse/CALCITE-3008?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16822783#comment-16822783
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Julian Hyde commented on CALCITE-3008:
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I don't really like the idea of a static {{AuxiliaryConverter}} that can handle
all functions. It would be monolithic - it would be difficult to add a
user-defined function and the ability to convert it.
So how about adding the following to {{SqlOperator}}:
{code}
<T> T unwrap(Class<T> clazz);
{code}
Then you would call {{function.unwrap(AuxiliaryConverter.class)}} on each
function. Thus each function knows how to convert itself.
Compare with {{RexSqlConvertlet}}, where there is also one instance for each
function. All of the convertlets are registered in a {{RexSqlConvertletTable}}.
Following that idea, maybe instead of {{unwrap}} we could add a method
{{SqlFunction getAuxiliaryConverter(SqlFunction)}} to {{SqlOperatorTable}}. At
least we have a way to chain operator tables together, which would make it
possible to add UDFs without having to recompile Calcite.
> Making AuxiliaryConverter Pluggable
> -----------------------------------
>
> Key: CALCITE-3008
> URL: https://issues.apache.org/jira/browse/CALCITE-3008
> Project: Calcite
> Issue Type: Improvement
> Components: core
> Reporter: Rong Rong
> Priority: Major
> Labels: pull-request-available
> Time Spent: 0.5h
> Remaining Estimate: 0h
>
> Currently the {{AuxiliaryConverter}} in calcite core is set to be static with
> only one basic implementation. It would be nice to have it pluggable so that
> other systems can implement its own.
> Was wondering if this would be a good feature to add?
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