Pact API Proposal: Add keyless CoGroup (send all to a single group)

[andrehacker]

I propose to add a keyless version of CoGroup that groups both inputs in a single group, analogous to the keyless Reducer version that was added in #61

CoGroupContract myCoGroup = CoGroupContract.builder(MyUdf.class)
    .input1(contractA)
    .input2(contractB)
    .build();

I have a use case where I need to process the output of two contracts in a single udf and I currently have to use the workaround to add a constant field and use this as grouping key.

Adding a keyless version would reduce the overhead (network traffic, serialization and code-writing) and give the compiler additional knowledge (The compiler knows that there will be only a single group and a single udf call. If setAvgRecordsEmittedPerStubCall is set, it could infer the output cardinality)

Furthermore I think this would be consequent, because CoGroup is like Reduce for multiple inputs.

[rmetzger]

We should implement this for the new Java API #463.

[StephanEwen]

I am actually not too sure about that one. Keyless reducers are mostly only
valuable if they are combinable. What would be the use case for a key-less
cogroup?
Am 20.03.2014 17:25 schrieb "Robert Metzger" notifications@github.com:

We should implement this for the new Java API #463#463
.

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