P2164R1 views::enumerate (Corentin Jabot)

A short summary of the feedback form ML, closed on 14 Sep 2020:

1. index's type should be replaced from difference_type to count_type .
   The bug was fixed on R2
2. enumerate's value_type should have range_value_t value, instead of range_reference_t value.
   The bug was fixed on R2
3. A suggestion to reconsider the return value of enumerate.
4. A suggestion to define enumerate(v) as zip(iota(0), v) instead of having enumerate as a standalone adapter (which will allow composing enumerate from another view)
   Author:

• zip is not yet in C++23 plans.
• zip is a heavier machinery. The current is simpler, lighter design, provides better diagnostics/compile time.

P2164R2 views::enumerate (Corentin Jabot)

This will probably get rolled into the upcoming "Plan for C++23 ranges" effort. We'll leave it separate for now, but it should be tagged for meeting review not mailing list review.

P2164R3 views::enumerate (Corentin Jabot)

2021-02-09 Library Evolution Telecon

P2164R3: views::enumerate

2021-02-09 Library Evolution Telecon Minutes

Summary

Some discussion was around having const members, which inhibit assignment. The general feeling was not to have them.

The larger discussion was around whether or not we want named fields at all vs. tuple. The arguments in favor of tuple is that otherwise there is a lot more that needs to be added (comparisons, cross conversions, etc.). The author was asked to come back with a revision containing a cost-benefit analysis of adding a new type with named fields for this.

Outcome

Bring a revision of P2164R3 (views::enumreate), with the guidance below, to Library Evolution for further design review.

• Compare and contrast having enumerate return an aggregate struct with named members versus a tuple so that Library Evolution can decide between the two approaches.

P2164R4 views::enumerate (Corentin Jabot)

Reviewed by SG9 at Kona2022 meeting (Full Minutes).

Polls

POLL: We would prefer the tuple solution for “P2164: views::enumerate” (which is the safer way).

Attendance: 15 (on-site 11, online 4)

# of Authors: 1

Author’s position: F

Outcome: Strong consensus in favor

POLL: We support applying the resolution of “FR#416: FR-014-021 26.6 (range.factories) Add views::enumerate (duplicate: US#525)”, and forward “P2164: views::enumerate” to C++23 with the proposed resolution.

Attendance: 15: 4 11

# of Authors: 1

Author’s position: SF

Outcome: Consensus in favor

A: Oppose to adding features by NB comments

Summary

The author has presented the paper. There was a design question - whether we want tuple (which was implemented and is the simpler solution) or an aggregate (which was not implemented, and expected to have difficulty in implementation). SG9 voted for tuple (the verified solution).

SG9 supports the resolution proposed in the NB comment - adopting P2164 to C++23 (with the design guidance - use tuple and not aggregate). Will be passed for LEWG's final decision.

The issue was forwarded to LEWG.

New version: https://isocpp.org/files/papers/D2164R8.pdf

LEWG discussed R8 of this paper at the 2022-11 Kona meeting (full minutes) and forwarded the paper (with the design recommendation to use tuple) for C++23. NB comment resolved as "accepted".

Polls

POLL: We want the “aggregate” solution over the “tuple” solution for “P2164: views::enumerate”

Attendance: 25 (20 onsite, 5 on-line)

# of Authors: 1xSA

Author Position: Consensus against

POLL: Apply the resolution of NB comment: “FR#416: FR-014-021 26.6 (range.factories) Add views::enumerate” (duplicate of: “US 48-108 26 [ranges] Add views::enumerate”) (issue: cplusplus/nbballot#416) for C++23

Attendance: 25 (20 onsite, 5 on-line)

# of Authors: 1xSF

Author Position: Consensus in favor

Summary

Author will update the paper according to LEWG's design recommendation, the paper will target C++23 (to be confirmed with electronic poll).

P2164R8 views::enumerate (Corentin Jabot)

LWG reviewed D2164R9 and approved P2164R9 for C++, ship vehicle to be confirmed by LEWG electronic poll.

P2164R9 views::enumerate (Corentin Jabot)

2022-11 Library Evolution Electronic Poll Outcomes

Poll 1.1: Send [P2164R8] views::enumerate to Library Working Group for C++23, classified as an addition ([P0592R4] bucket 3 item).

Outcome: Consensus in favor.

Ship vehicle is confirmed to be c++23 so marking tentatively ready for plenary