Xavier Léauté created KAFKA-4481:
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Summary: Relax Kafka Streams API type constraints
Key: KAFKA-4481
URL: https://issues.apache.org/jira/browse/KAFKA-4481
Project: Kafka
Issue Type: Improvement
Components: streams
Reporter: Xavier Léauté
Assignee: Xavier Léauté
Streams API methods that apply transformations to streams are currently
invariant in the key and value types, when they should probably be
contravariant in those types.
For instance, {{KStream.filter(Predicate<K, V> predicate)}} should be
{{KStream.filter(Predicate<? super K, ? super V> predicate)}} to accept
predicates that can act on any supertype of K, or V.
Same thing applies to method that take {{Aggregator}}s, {{StreamPartitioner}}s,
{{KeyValueMapper}}s, {{ValueMapper}}s, {{ProcessorSupplier}}s,
{{ValueJoiner}}s, etc.
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