Github user xccui commented on the issue:
https://github.com/apache/flink/pull/5032
Thanks for the suggestion @aljoscha.
The problem is the state type is provided via a generic type parameter `S
extends State`, which will be erased in runtime. Thus it's hard to do type
checking in `AbstractKeyedStateBackend` unless we explicitly store and check
the type for each state name (and that may affect the performance). The
existing "leave alone" solution seems to be the most efficient way, but we can
only get a `ClassCastException` with that. What do you think?
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