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https://issues.apache.org/jira/browse/CALCITE-1434?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15586343#comment-15586343
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Julian Hyde commented on CALCITE-1434:
--------------------------------------
I've pushed a snapshot based on
https://github.com/apache/calcite/commit/d9e9103bb1dec32f41eee8e4d2b4aa11b35a2d5d.
Releases occur about every 6-8 weeks, but no one has committed to a date right
now. If you have opinions when you would like a release, please start a thread
on dev.
> User-defined aggregate function that uses a generic interface
> -------------------------------------------------------------
>
> Key: CALCITE-1434
> URL: https://issues.apache.org/jira/browse/CALCITE-1434
> Project: Calcite
> Issue Type: Bug
> Reporter: Arun Mahadevan
> Assignee: Julian Hyde
> Fix For: 1.11.0
>
>
> {{AggregateFunctionImpl}} doesn't work if the class implements a generic
> interface. We have an interface like below which we want to expose to users
> for writing aggregate functions.
> {noformat}
> public interface UDAF<A, V, R> {
> A init();
> A add(A aggregate, V val);
> R result(A aggregate);
> }
> {noformat}
> Internally we create an instance of {{AggregateFunctionImpl}} and register
> the Function in {{SchemaPlus}}. However this doesn't work for example if we
> have an implementation like below,
> {noformat}
> public class MySum implements UDAF<Number, Number, Number> {
> @Override
> public Number init() {...}
> @Override
> public Number add(Number aggregate, Number val) {...}
> @Override
> public Number result(Number aggregate) {...}
> }
> {noformat}
> We get an Exception "java.lang.RuntimeException: In user-defined aggregate
> class 'x.y.z.$MySum', first parameter to 'add' method must be the accumulator
> (the return type of the 'init' method)"
> This happens because the ReflectiveFunctionBase.findMethod is trying to look
> for a method name "init" and it get a method with a different signature (that
> returns Object) instead of the actual method defined in MySum. This happens
> to be a 'bridge' method inserted by java.
> In findMethod, the bridge methods can be skipped while looking for the method
> by name.
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