presto-main/src/main/java/io/prestosql/operator/aggregation/DecimalSumAggregation.java/DecimalSumAggregation/specialize
class DecimalSumAggregation:    @Override
    public InternalAggregationFunction specialize(BoundVariables boundVariables, int arity, Metadata metadata)
    {
        Signature signature = getFunctionMetadata().getSignature();
        Type inputType = metadata.getType(getOnlyElement(applyBoundVariables(signature.getArgumentTypes(), boundVariables)));
        Type outputType = metadata.getType(applyBoundVariables(signature.getReturnType(), boundVariables));
        return generateAggregation(inputType, outputType);
    }