Daniel Mills created BEAM-1276:
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Summary: 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:
@StateId("count")
private final StateSpec<Object, AccumulatorCombiningState<Integer, int[],
Integer>> countSpec =
StateSpecs.combiningValue(
Sum.ofIntegers().getAccumulatorCoder(pipeline.getCoderRegistry(),
VarIntCoder.of()), Sum.ofIntegers());
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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