Github user walterddr commented on the issue:
https://github.com/apache/flink/pull/5555
I agree this design is much cleaner and easier to maintain later. I was
hesitating to change the function signature of `generateAggregations()`.
I will try to introduce some common building blocks and handle
implementation effort in codegen. I will imagine a lot of ITCases will be
needed :-)
Thanks for the feedback @hequn8128 @fhueske ---
