feat: add `Iter.enumerate` method

[q-uint]

Takes an iterator and returns a new iterator that produces the same elements with corresponding indices.

import Iter "mo:base/Iter"; 

let letters = [ "a", "b", "c" ];
let enumeratedIter = Iter.enumerate(letters.vals());
assert(?(0, "a") == enumeratedIter.next());
assert(?(1, "b") == enumeratedIter.next());
assert(?(2, "c") == enumeratedIter.next());
assert(null == enumeratedIter.next());

Simplifies:

var i = 0;
for (l in letters.vals()) {
  // Do somthing with `i` and `l`.
  i += 1;
}

[dfinity-droid-prod[bot]]

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[ByronBecker]

@kentosugama @crusso Would love to see this merged in - sometimes just need a count aware iterator without needing to provide a function (like in Iter.iterate)

[dfinity-droid-prod[bot]]

Dear @q-uint,

In order to potentially merge your code in this open-source repository and therefore proceed with your contribution, we need to have your approval on DFINITY's CLA[^1].

If you decide to agree with it, please visit this issue and read the instructions there.

— The DFINITY Foundation [^1]: Contributor License Agreement

[ggreif]

Let me ask an innocent question... Isn't this just a zip of the passed-in iterator with some unbounded range?

[q-uint]

Isn't this just a zip of the passed-in iterator with some unbounded range?

In a way yes, currently only the List and Buffer structs have the zip operation defined afaik. Might be interesting to also support this for iterators.

[crusso]

@kentosugama @ggreif any reason not to merge this?

[ggreif]

I am a bit concerned about

• utility: this is a very specific function
• heap traffic: this tends to create a lot of pairs in the heap that end up as garbage
• naming: this really enumerating things?

IMHO what we need is a rangeFrom iterator that gives the naturals (open ended) and then zips it with the above letters.vals().

[q-uint]

Seems like there aren't any plans to merge this.