[jira] [Created] (BEAM-247) CombineFn's only definable/usable inside sdk.transforms package

["Ben Chambers (JIRA)" <ji...@apache.org>]

Ben Chambers created BEAM-247:
---------------------------------

             Summary: CombineFn's only definable/usable inside sdk.transforms package
                 Key: BEAM-247
                 URL: https://issues.apache.org/jira/browse/BEAM-247
             Project: Beam
          Issue Type: Bug
          Components: sdk-java-core
            Reporter: Ben Chambers
            Assignee: Pei He
            Priority: Critical


{code:java}
public abstract static class CombineFn<InputT, AccumT, OutputT>
  extends AbstractGlobalCombineFn<InputT, AccumT, OutputT> { /* ... */ }
abstract static class AbstractGlobalCombineFn<InputT, AccumT, OutputT>
  implements GlobalCombineFn<InputT, AccumT, OutputT>, Serializable { /* ... */ }
{code}

Since {{AbstractGlobalCombineFn}} is package protected (and therefore not visible outside of the {{transform}} package, it is not possible to cast any class that extends {{CombineFn}} to a {{GlobalCombineFn}} outside of this package.

This prevents applying existing {{CombineFn}}s directly (such as {{Combine.perKey(new Sum.SumIntegersFn())}}, as used in our documentation) and also means that a user cannot define their own {{CombineFn}} unless they put them in the {{transform}} package.



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