[jira] [Commented] (BEAM-1276) StateSpecs.combiningValue interface is very awkward to use

["Kenneth Knowles (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/BEAM-1276?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15826813#comment-15826813 ] 

Kenneth Knowles commented on BEAM-1276:
---------------------------------------

Agree tremendously. I would propose the following approach generally:

1. A new interface named TBD where the accumulator type is fixed and known by the function itself. I'll choose a terrible name to be sure it is renamed: {{MonomorphicCombineFn}} that has a parameterless {{getAccumulatorCoder()}} method.
2. Any {{CombineFn}} that does not require the input type or coder registry ported to implement this interface.
3. {{StateSpecs.combiningValue(MonomorphicCombineFn)}} that makes it easy to use with state.

> StateSpecs.combiningValue interface is very awkward to use
> ----------------------------------------------------------
>
>                 Key: BEAM-1276
>                 URL: https://issues.apache.org/jira/browse/BEAM-1276
>             Project: Beam
>          Issue Type: Bug
>          Components: sdk-java-core
>            Reporter: Daniel Mills
>            Assignee: Kenneth Knowles
>            Priority: Minor
>
> Using StateSpecs.combiningValue with built in combiners is very verbose.  For example, to keep a running sum of ints:
> {code}
> @StateId("count")
> private final StateSpec<Object, AccumulatorCombiningState<Integer, int[], Integer>> countSpec =
>     StateSpecs.combiningValue(
>           Sum.ofIntegers().getAccumulatorCoder(pipeline.getCoderRegistry(), VarIntCoder.of()), Sum.ofIntegers());
> {code}
> This involves getting a reference to the pipeline into the DoFn, guessing/finding the proper type parameters for Sum.ofIntegers(), and manually pulling the accumulator coder out.
> For combiners like Sum.ofIntegers() that have a fixed accumulator, the combiningValue call should be able to deduce that.  Additionally, it would be nice to remove the type of the accumulator from the StateSpec object, since the user only needs the input and output types in their code.



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