Numeric (and accumulators)

[Joe Darcy]

On 9/17/2012 8:37 AM, Brian Goetz wrote:
>>> These guys also need companion classes that are mutable,
>>
>> Like for example Atomic{Integer,Long}? :-)
>
> So, writing out the complete set of candidate numeric types that have 
> been proposed (we can prune them later):
>
>  - New interface BoxedPrimitive extends Number (Joe)
>  - New interface Numeric<BoxedPrimitive> (Doug)
>  - Mutable implementation classes of Numeric (Brian)
>  - Complete the set of atomic implementation classes (Doug)
>  - Accumulator classes (Doug)
>
> I'll just say that we don't need to get caught up in premature 
> either/or; if all of these are worth having, we can have them.
>
>> public abstract class LongAccumulator implements Numeric<Long> {
>
> I like these.  I believe that they all assume commutative combination 
> functions, not simply associative (what are sometimes called abelian 
> monoids, rather than ordinary monoids)?

For a "DoubleAccumulator", I'll just note that a good implementation 
will need to maintain some internal state.  To have a reasonably good 
chance of getting a robustly accurate double sum, extra work is needed 
over just "sum += d[i++]."  One pretty simply approach is called 
compensated summation.  People have also looked at sorting the input, etc.

-Joe