[Pre-RFC] Replace IteratorExt::zip with tuple iteration

[bluss]

I prefer the explicit versions like (a, b, c).zip() or Zip::new((a, b, c)) too.

[lambda-fairy]

@glaebhoerl

Probably my Haskell showing, but my first instinct was to interpret this as a cartesian product ((1,2,3), (1,2,4), (1,2,5) ... (1,2,13), (1,3,3), (1,3,4), ... etc.) rather than a zip.

Yeah, there are at least four ways to interpret (a, b, c).into_iter():

1. Zip the iterators (original proposal)
2. Chain the iterators
3. Cartesian product (@glaebhoerl, Haskell)
4. Treat the tuple as a slice (@DanielKeep, Python)

Without context, it won't be obvious which of these is being used.

[oli-obk]

tuple as slice won’t make sense if the type of the tuple elements differs, and would then make sense for all types (even those that don’t implement Iterator.

I now agree that there should be a TupleIterExt that offers .zip() and .prod() for all tuples of types implementing Iterator.

.chain() is special, as it can only exist if the iterators have the same Item type.

[hauleth]

but to have it possible in sane way we need variadic templates.

[oli-obk]

since this has been delegated to post-1.0 we can wait for variadic generics