quantity[Int, A] extension on Iterator[A], quantity[Long, A] on a F[A]: Foldable ?

[benhutchison]

If our Data Types are units, then it would seem that a collection's size ought to yield a typed Quantity. A quantity extension method could be offered over sized-collections eg

• Iterator and the Scala collections API
• Cats Foldable

These would presumably be in separate modules since they are distinct from other Coulomb features

[erikerlandson]

@benhutchison yes, this has been on my to-do list for a long time. In scala 3 they redesigned the "internals" of scala's collection library, and I need to get familiar with how these all work to best integrate with the collections lib.

xref: #50

But yes, there should be a .qlength or .ulength that returns Quantity[Int, A] for any Seq[A] - this bit would be easy, just an extension method.

[benhutchison]

Some sort of qsum operation for Collections of Quantitys would also be useful. The existing sum requires a Numeric and it isn't possible to implement Numeric[Quantity[V, U]] (Yes I tried :P).

[benhutchison]

Actually @erikerlandson , when I tried defining a qsum: Quantity[V, U] over an Iterable[Quantity[V, U]], I ran into the problem of needing a zero: Quantity[V, U] operation to begin the sum fold with.

Have you thought about providing a zero (and possibly one) type-class for quantities?

[erikerlandson]

Yes, Numeric isn't possible, quantities aren't type-closed under multiplication. I think you could get away with defining AdditiveGroup, which includes a zero.

Ironically, RuntimeQuantity would work more easily here since the unit type is RuntimeUnit and it has no type closure problems.