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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