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https://issues.apache.org/jira/browse/KAFKA-8035?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Bruno Cadonna updated KAFKA-8035:
---------------------------------
Summary: Add tests for generics in KStream API (was: Add tests for
generic bounds for KStream API )
> Add tests for generics in KStream API
> --------------------------------------
>
> Key: KAFKA-8035
> URL: https://issues.apache.org/jira/browse/KAFKA-8035
> Project: Kafka
> Issue Type: Test
> Components: streams
> Reporter: Bruno Cadonna
> Priority: Major
>
> During the work on KAFKA-4217, it was discovered that some combinations of
> Java generics block the usage of lambda functions ([see this
> discussion|https://github.com/apache/kafka/pull/5273#discussion_r216810275]).
> To avoid using those blocking combinations of generics, tests shall be
> implemented that verify that lambda functions can be used with the KStream
> API. Those tests may also serve as regression tests to ensure that future
> changes to the generics in the KStream API may not block lambda functions and
> make the API incompatible with previous versions.
> Unlike other tests, the tests required here pass if they compile. For
> example, to verify that the parameter {{mapper}} in
> {code:java}
> <KR, VR> KStream<KR, VR> flatMap(final KeyValueMapper<? super K, ? super V, ?
> extends Iterable<? extends KeyValue<? extends KR, ? extends VR>>> mapper);
> {code}
> accepts a {{KeyValueMapper}} specified as a lambda function that returns an
> implementation of the {{Iterable}} interface, the following stream could be
> specified in the test:
> {code:java}
> stream
> .flatMap((Integer key, Integer value) -> Arrays.asList(
> KeyValue.pair(key, value),
> KeyValue.pair(key, value),
> KeyValue.pair(key, value)))
> .foreach(action);
> {code}
> If the test compiles, the test passes.
> Other tests for {{flatMap}} need to check the bounds of the generics, e.g.,
> if the {{mapper}} accepts a {{KeyValueMapper}} specified as a lambda function
> that takes a super class of K and V as inputs.
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