Add Windows-like Iterator that returns static-sized tuple elements instead of slices. about itertools

[bluss]

Like in #151, I think for (fst, snd) in primes.iter().tuple_windows() can become a reality soon.

[bluss]

I don't think typenum supports tuples, or is the solution we want? We can do something simpler with traits. Should look at other cases like .combinations() as well as windows.

[bluss]

Needs to take into account that integer parameters like 2 are runtime information and tuple arity is type-level compile time information. Would work fine with a type-level kind of parameterization, either .windows2() or .windows::<Pair>() and so on.

[Robbepop]

Ah dang. You are right, I haven't thought about that. Maybe with the typenum crate one could work around this until associated constants land in Rust, if ever?

[Robbepop]

I do not know exactly how he did it, but in Crate: Generic Array the owner uses typenum::uint in order to create a generic statically sized array. This could be used in a similar way to create an easy-to-use windows(N) iterator that can have tuples (compile-time-constant size types) as iterator elements. =)
ArrayLength is where the magic happens according to the owner of the generic-array crate.

[bluss]

They use an interesting trick where they just make a struct of the correct size. Instead of [T; 4] they have struct { struct { T, T }, struct { T, T } }.

[mmun]

I was looking for this today and my gut reaction was to try

let primes = &[2, 3, 5, 7, 11, 13, 17, ...];
for (fst, snd) in iwindow!(primes.iter(), 2) {
    println!("({}, {})", fst, snd);
}