Make a Product adapter for the Itertools trait about itertools HOT 5 CLOSED

An adaptor for product is a good idea, I guess it's the most natural way to use it. Not sure if we can make it expand tuples like the iproduct macro does (((x, y), z) → (x, y, z)).

from itertools.

That would be preferable, but I think it requires variadic generics, or at minimum having two impls, one for Item=A and one for Item=(A,B).

I'd be satisfied with the basics for now. I can always map(|((x,y),z)| (x,y,z)) until then.

from itertools.

Is there any reason to prefer the long name cartesian_product? I.e. are there other products we might want to add?

from itertools.

@bluss Can't think of any others (not that there aren't any), but we want to avoid product() because it's taken by MultiplicativeIterator. times() would work too, though it's less specific.

from itertools.

Something else very useful is a Cartesian product without a hardcoded length, i.e., concretely something like taking a vector of iterators and returning a iterator of vectors: a form of Haskell's sequenceA, where

sequenceA [[0..2], [0..2], [0..2]] == [[0,0,0],[0,0,1],[0,0,2],[0,1,0],[0,1,1],[0,1,2],[0,2,0],[0,2,1],[0,2,2],[1,0,0],[1,0,1],[1,0,2],[1,1,0],[1,1,1],[1,1,2],[1,2,0],[1,2,1],[1,2,2],[2,0,0],[2,0,1],[2,0,2],[2,1,0],[2,1,1],[2,1,2],[2,2,0],[2,2,1],[2,2,2]]

from itertools.