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From Xavier Léauté (JIRA) <j...@apache.org>
Subject [jira] [Updated] (KAFKA-4672) KIP-100 api changes break Java 8 lambda expressions in some cases
Date Wed, 18 Jan 2017 22:06:26 GMT

     [ https://issues.apache.org/jira/browse/KAFKA-4672?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Xavier Léauté updated KAFKA-4672:
---------------------------------
    Description: 
Variance changes introduced in KIP-100 cause compilation failures with lambda expression in
Java 8.

To my knowledge this only affects methods taking suppliers of functions
KStreams.transform(TransformerSupplier<...>, String...)
KStreams.transformValues(ValueTransformerSupplier<...>)

prior to the changes it was possible to write

streams.transform(MyTransformer::new)
streams.transformValues(MyValueTransformer::new)

where MyTransformer and MyValueTransformer extend Transformer and ValueTransformer respectively.

After the changes the Java compiler is unable to infer correct return types for the lambda
expression.

  was:
Variance changes introduced in KIP-100 cause compilation failures with lambda expression in
Java 8.

To my knowledge this only affects methods taking suppliers of functions
KStreams.transform(TransformerSupplier<...>, String...)
KStreams.transformValues(ValueTransformerSupplier<...>)
KStreams.process(ProcessorSupplier<...>)

prior to the changes it was possible to write

streams.process(MyProcessor::new)
streams.transform(MyTransformer::new)
etc.

where MyProcessor and MyTransformer extend Processor and Transformer respectively.

After the changes the Java compiler is unable to infer correct types for the lambda expression.


> KIP-100 api changes break Java 8 lambda expressions in some cases 
> ------------------------------------------------------------------
>
>                 Key: KAFKA-4672
>                 URL: https://issues.apache.org/jira/browse/KAFKA-4672
>             Project: Kafka
>          Issue Type: Bug
>          Components: streams
>    Affects Versions: 0.10.2.0
>            Reporter: Xavier Léauté
>            Assignee: Xavier Léauté
>             Fix For: 0.10.2.0
>
>
> Variance changes introduced in KIP-100 cause compilation failures with lambda expression
in Java 8.
> To my knowledge this only affects methods taking suppliers of functions
> KStreams.transform(TransformerSupplier<...>, String...)
> KStreams.transformValues(ValueTransformerSupplier<...>)
> prior to the changes it was possible to write
> streams.transform(MyTransformer::new)
> streams.transformValues(MyValueTransformer::new)
> where MyTransformer and MyValueTransformer extend Transformer and ValueTransformer respectively.
> After the changes the Java compiler is unable to infer correct return types for the lambda
expression.



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