LWG4476. run_loop should not have a set_error completion

[jwakely]

https://cplusplus.github.io/LWG/issue4476

This issue proposes adding noexcept to the run() and finish() members, which have narrow contracts. Violating the preconditions would be a logic error in the program; users of the run_loop scheduler should not try to run it when it's in the wrong state.

LWG would like to get LEWG confirmation that violating the Lakos Rule is appropriate here.

See also https://cplusplus.github.io/LWG/issue4215 which gives additional rationale for run_loop::finish() being non-throwing, by analogy with destructors.

[inbal2l]

2026-03-27 LEWG Croydon Meeting

• LWG4476. run_loop should not have a set_error completion (C++26)
• LWG4361. awaitable-receiver::set_value should use Mandates instead of constraints (C++26)
• P4151 R0 Rename affine_on (C++26)
• P3666 R3 Bit-precise integers (C++29)

2026-03-27 Library Evolution Croydon Minutes - session 1

Champion(s): Eric / Robert / Dietmar / Jan
Chair: Fabio / Inbal
Minute Taker(s): Robert

Summary

POLL: Follow the resolution of LWG4476 (remove set_error from run_loop) and forward to LWG for C++26

SF	F	N	A	SA
4	10	0	0	0

Attendance: 19 (IP) + 5 (R)
Author's Position: N/A
Outcome: Consensus in favor.

POLL: Following the resolution of “LWG4361. awaitable-receiver::set_value should use Mandates instead of constraints”, we support turning the receiver_of & sender_to concepts into exposition only concepts and forward the resolution to LWG for C++26

SF	F	N	A	SA
5	7	0	0	0

Attendance: 19 (IP) + 5 (R)
Author's Position: N/A
Outcome: Consensus in favor.

POLL: Forward P4151R0 (rename affine_on to affine) to LWG for C++26

SF	F	N	A	SA
7	7	0	0	0

Attendance: 22 (IP) + 4 (R)
Author's Position: SF
Outcome: Consensus in favor.

POLL: We should prevent library support for _BitInt

SF	F	N	A	SA
5	9	2	3	1

Attendance: 21 (IP) + 4 (R)
Author's Position: SA
Outcome: Consensus in favor.

POLL: std::is_integral_v<_BitInt(N)> should be false

SF	F	N	A	SA
7	4	5	2	0

Attendance: 21 (IP) + 4 (R)
Author's Position: N/A
Outcome: Consensus in favor.

POLL: We should provide alias templates for _BitInt() (i.e. std::bit_int and std::bit_uint – possibly under a different name e.g. std::cbit_int)

SF	F	N	A	SA
0	3	8	3	5

Attendance: 21 (IP) + 4 (R)
Author's Position: N/A
Outcome: No Consensus.

POLL: We should provide std::bit_int and std::bit_uint as class templates (not necessarily as part of P3666)

SF	F	N	A	SA
2	4	8	4	0

Attendance: 21 (IP) + 4 (R)
Author's Position: WA
Outcome: No Consensus.

Next Steps

• LWG4476 remove set_error from run_loop - Approved (C++26)
• LWG4361. awaitable-receiver::set_value should use Mandates instead of constraints - Approved (with change) (receiver_of & sender_to being exp only concepts) (C++26)
• P4151R0: rename affine_on to affine - Approved (C++26)
• P3666R3: Bit-precise integers - Feedback given, will be seen again. (C++29)
  • Room prefer minimal support in the type (prevent library support for _BitInt, std::is_integral_v<_BitInt(N)> should be false, no alias).
  • There was also no appetite for class templated (in the future) e.g. std::bit_int and std::bit_uint.

[inbal2l]

2026-03-27 LEWG Croydon Meeting

• LWG4476. run_loop should not have a set_error completion (C++26) (session 2)

See: #2265 (comment)

Status: Re-discssed, Approved (C++26)