Github user tillrohrmann commented on the pull request:
https://github.com/apache/flink/pull/814#issuecomment-114232368
The subtypes of `Writable` are still serialized using the special
`Writable` serializer. However, there are situations where you only have a
`Writable` type, e.g. for the Mahout DSL or if you have `DataSet` of
`LongWritable` and `TextWritable`.. Why should we not allow to use the
interface type then?
---
If your project is set up for it, you can reply to this email and have your
reply appear on GitHub as well. If your project does not have this feature
enabled and wishes so, or if the feature is enabled but not working, please
contact infrastructure at infrastruct...@apache.org or file a JIRA ticket
with INFRA.
---
