Arun Mahadevan created CALCITE-1434:

             Summary: AggregateFunctionImpl doesnt work if the class implements 
a generic interface
                 Key: CALCITE-1434
             Project: Calcite
          Issue Type: Bug
            Reporter: Arun Mahadevan
            Assignee: Julian Hyde

We have an interface like below which we want to expose to users for writing 
aggregate functions.

public interface UDAF<A, V, R> {
    A init();
    A add(A aggregate, V val);
    R result(A aggregate);

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,

public class MySum implements UDAF<Number, Number, Number> {
    public Number init() {...}
    public Number add(Number aggregate, Number val) {...}
    public Number result(Number aggregate) {...}

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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