Github user greghogan commented on the issue:
https://github.com/apache/flink/pull/2294
This would replace `Delegate` and is much simpler. I placed it in the Java
API package but it would not be visible to users through the `DataSet` API.
The ultimate goal is to implicitly reuse operations performing the same
computation on the same input `DataSet`. The optimizer cannot do this without
understanding the UDF configuration and logic. Two instances of a UDF may be
* incompatible, in which case a new result must be computed
* the same, in which case the old result can be reused
* different but compatible, in which case the UDF can merge the
configurations and the new, shared result replaces the old result
Replacing the old result requires a wrapper. Using `ProxyFactory` in
`Delegate` has limitations as documented in FLINK-4257. With a `NoOpOperator`
we can perform the same function by appending and then ignoring a dummy POJO
operator.
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