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Posted to dev@kafka.apache.org by "Xavier Léauté (JIRA)" <ji...@apache.org> on 2016/12/02 22:15:58 UTC
[jira] [Updated] (KAFKA-4481) Relax Kafka Streams API type
constraints
[ https://issues.apache.org/jira/browse/KAFKA-4481?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Xavier Léauté updated KAFKA-4481:
---------------------------------
Description:
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}}, {{StreamPartitioner}}, {{KeyValueMapper}}, {{ValueMapper}}, {{ProcessorSupplier}}, {{ValueJoiner}}, etc.
was:
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.
> 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
> Labels: usability
>
> 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}}, {{StreamPartitioner}}, {{KeyValueMapper}}, {{ValueMapper}}, {{ProcessorSupplier}}, {{ValueJoiner}}, etc.
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