Tabulators, reducers, etc

[Brian Goetz]

You are correct that this is mostly sugar around forEach.  But we want 
to enable the same sort of flexible, composible operation for concurrent 
accumulations.  If the user wants to do a three-level groupBy, writing 
the Block for this is ugly, and we want users to be able to reuse canned 
tabulations like groupBy, partition, etc.

If that means a thin layer around forEach (just as now tabulate is a 
thin layer around reduce), that's fine.  If it means we use forEach, but 
have combinators for constructing the appropriate blocks, that's fine 
too.  That's exactly the discussion I'd like to have surrounding 
concurrent accumulation.


On 12/31/2012 1:17 PM, Remi Forax wrote:
> On 12/31/2012 07:08 PM, Brian Goetz wrote:
>>> One option might be: use "reduce" for the purely functional forms, use
>>> accumulate/accumulateConcurrent for the others:
>>>
>>>      T reduce(T zero, BinaryOperator<T> reducer);
>>>      Optional<T> reduce(BinaryOperator<T> reducer);
>>>      <U> U reduce(U zero, BiFunction<U, T, U> accumulator,
>>> BinaryOperator<U> reducer);
>>>
>>>      <R> R accumulate(Accumulator<T, R> reducer);
>>>      <R> R accumulate(Supplier<R> seedFactory,
>>>                       BiBlock<R, T> accumulator,
>>>                       BiBlock<R, R> reducer);
>>>
>>>      <R> R accumulateConcurrent(ConcurrentAccumulator<T, R> tabulator);
>>>
>>>    This would let us get rid of the Tabulator abstraction (it is
>>> identical to MutableReducer; both get renamed to Accumulator).
>>> Separately, with a small crowbar, we could simplify
>>> ConcurrentAccumulator down to fitting into existing SAMs, and the
>>> top-level abstraction could go away.
>>
>> While the concurrent use case is clearly the odd man out here --
>> suggesting more work is left to do on this -- the rest of it seems an
>> improvement on what we have now.  I would like to move forward with
>> this while we continue to work out the correct set of canned
>> accumulators and the correct way to surface concurrent accumulation.
>
> while do you want to surface concurrent accumulator given that we have
> forEach ??
>
> Rémi
>