Josh Lemer created FLINK-9221:
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Summary: Add method SinkFunction[A]#contramap[B](f: B => A):
SinkFunction[B]
Key: FLINK-9221
URL: https://issues.apache.org/jira/browse/FLINK-9221
Project: Flink
Issue Type: Task
Reporter: Josh Lemer
Just like it is very useful to use `DataStream[T]` as a sort of Functor or
Monad with `map`/`flatMap`/`filter` methods, it would be extremely handy to
have a `SinkFunction[A]#contramap[B](f: B => A): SinkFunction[B]` on
`SinkFunctions`, so that you can reuse existing complex sink functions, but
with a different input type. For example:
{code}
val bucketingStringSink: SinkFunction[String] =
new BucketingSink[String]("...")
.setBucketr(new DateTimeBucketer("yyyy-MM-dd-HHmm")
val bucketingIntListSink: SinkFunction[List[Int]] =
bucketingStringSink.contramap[List[Int]](_.mkString(","))
{code}
For some more formal motivation behind this,
https://typelevel.org/cats/typeclasses/contravariant.html is definitely a great
place to start!
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