P2321R2 `zip`

[StephanTLavavej]

P2321R2 zip

Feature-test macro:

#define __cpp_lib_ranges_zip 202110L

Be sure to implement the resolutions of these LWG issues which patch this feature:

• LWG-3692 zip_view::iterator's operator<=> is overconstrained
• LWG-3702 Should zip_transform_view::iterator remove operator<?
• LWG-3773 views::zip_transform still requires F to be copy_constructible when empty pack
• LWG-3798 Rvalue reference and iterator_category
  • Affects views::adjacent_transform, see [range.adjacent.transform.iterator]/1.1.
• LWG-3848 adjacent_view, adjacent_transform_view, and slide_view missing base accessor

and the pertinent changes from P2165R4 and P2494R2.

[Ukilele]

Not that I would want to make promises, that I will create a MR any time soon. But I at least implemented some of the minor changes as well as zip_view in https://github.com/Ukilele/STL/tree/ranges_zip.
I could use some help with:

• 5.1 & 5.2: Constructors and assignment operators for std::tuple and std::pair
• 5.4: Not sure which changes this requires
• 5.6: Is implemented as described in the paper. But are there functions whose noexceptness should be strengthened?

[frederick-vs-ja]

• 5.4: Not sure which changes this requires

Changes (or clarifications) in this section can be skipped now. They are superseded by WG21-P2393, which should be treated as a DR against C++20, and has already been implemented in MSVC STL.

[miscco]

Hey do you need any help with this?

[Ukilele]

Hey @miscco , I assume this question is addressed to me? If so, thanks for asking! Unfortunately, currently I wont find the time to work on this. The missing parts in my branch are noexcept-strengthening, unit tests as well as adjacent and adjacent_transform.

[miscco]

Note that you do not need to implement everything in a go.

Could you do a squash and rebase on main? I would be happy to give it another round of review and Tam implemented most prerequisites

[Ukilele]

Squashed and rebased on main 🙂
main...Ukilele:ranges_zip

[frederick-vs-ja]

P2165R4 also changes zip_view etc. (making them no longer use pair) and basic_common_reference and common_type partial specializations.

[CaseyCarter]

P2165R4 also changes zip_view etc. (making them no longer use pair) and basic_common_reference and common_type partial specializations.

I will add a note to the OP to make sure that zip implementation doesn't miss the changes from P2165R4. There's enough to P2165R4 that I think of it as more a standalone feature than simply a patch on zip, so I'll leave the separate feature issue.