LWG3714 Non-single-argument constructors for range adaptors should not be explicit

[jwakely]

Issue: https://cplusplus.github.io/LWG/issue3714

During the LWG prioritization poll it was suggested that we need LEWG to decide on a consistent policy before we can make any consistency fix here. Please take a look and let us know what LEWG wants here.

[billy-baker]

2022-07-19 Library Evolution Telecon

LWG3714: Non-single-argument constructors for range adaptors should not be explicit

2022-07-19 Library Evolution Telecon Minutes

Chair: Billy Baker

Minute Taker:

Champion: Hewill Kang

Summary

The topic was presented in the LEWG 2022-07-19 telecon. For consistency, the views listed in the issue as well as views that are in flight such as P2374 cartesian_product_view need to be reviewed. There was some previous discussion on the topic of explicit constructors for P1899 stride_view. The issue has been referred to the Ranges Study group for guidance.

Next Steps

Send the issue to the Ranges study group for further review.

[inbal2l]

Scheduled for SG9 on 10-10-2022 (Agenda)

[inbal2l]

SG9 (Ranges) reviewed the issue on 2022-10-10, the review included Ville's paper on the same subject PXXXXR0: Ruminations on explicit multi-param constructors of views (Full Minutes).

Polls

POLL: We support applying “LWG3714: Non-single-argument constructors for range adaptors should not be explicit” AKA option 2 in Ville’s paper: “Drop the explicit from the C++23 views” to C++23 (possibly as an NB comment, if needed)

SF	F	N	A	SA
1	4	3	2	0

Attendance: 10

Author’s position: SF

Outcome: Weak recommendation in favor (no consensus)

POLL: We support apply option 1 in Ville’s paper: “Make the C++20 view multi-param constructors explicit too” to C++20

SF	F	N	A	SA
0	6	3	0	0

Attendance: 10

Author’s position: WF

Outcome: Consensus in favor

Summary

The second poll had more consensus. The polls indicate that SG9 support making the C++20 view multi-param constructors explicit (as a C++20 DR / Fix), recommendation is passed to LEWG.