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4471. Remove test for get_env noexcept-ness from inline_scheduler

Section: 33.13.4 [exec.inline.scheduler] Status: New Submitter: Eric Niebler Opened: 2025-11-05 Last modified: 2026-01-16

Priority: 4

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Discussion:

33.13.4 [exec.inline.scheduler] bullet (3.2) reads:

get_env(sndr) is never potentially-throwing because it mandates that sndr.get_env() cannot throw, see 33.5.4 [exec.get.env].

also, get_completion_scheduler<set_*_t>(attrs) mandates that attrs.query(get_completion_scheduler<set_*_t>) cannot throw.

[2026-01-16; Reflector poll.]

Set priority to 4 after reflector poll.

"33.12.1.2 [exec.run.loop.types] (7.2) has the same redundancy."

Previous resolution [SUPERSEDED]:

This wording is relative to N5014.

  1. Modify 33.13.4 [exec.inline.scheduler] as indicated:

    -3- Let sndr be an expression of type inline-sender, let rcvr be an expression such that receiver_of<decltype((rcvr)), CS> is true where CS is completion_signatures<set_value_t()>, then:

    • (3.1) — the expression connect(sndr, rcvr) has type inline-state<remove_cvref_t<decltype((rcvr))>> and is potentially-throwing if and only if ((void)sndr, auto(rcvr)) is potentially-throwing, and
    • (3.2) — the expression get_completion_scheduler<set_value_t>(get_env(sndr)) has type inline_scheduler and is potentially-throwing if and only if get_env(sndr) is potentially-throwing.

[2026-01-16; Jonathan provides updated wording]

LWG believes the original issue discussion is wrong to say that get_env(sndr) can never throw, because the expression sndr itself could throw. However, we already state that get_env and get_completion_scheduler do not throw, so it's redundant to say that get_completion_scheduler(get_env(sndr)) only throws if sndr throws. If nothing except sndr in that expression is allowed to throw, then it's just stating the obvious.

Proposed resolution:

This wording is relative to N5032.

  1. Modify 33.13.4 [exec.inline.scheduler] as indicated:

    -3- Let sndr be an expression of type inline-sender, let rcvr be an expression such that receiver_of<decltype((rcvr)), CS> is true where CS is completion_signatures<set_value_t()>, then:

    • (3.1) — the expression connect(sndr, rcvr) has type inline-state<remove_cvref_t<decltype((rcvr))>> and is potentially-throwing if and only if ((void)sndr, auto(rcvr)) is potentially-throwing, and
    • (3.2) — the expression get_completion_scheduler<set_value_t>(get_env(sndr)) has type inline_scheduler and is potentially-throwing if and only if get_env(sndr) is potentially-throwing.

  2. Modify 33.12.1.2 [exec.run.loop.types] as indicated:

    -7- Let sndr be an expression of type run-loop-sender, let rcvr be an expression such that receiver_of<decltype((rcvr)), CS> is true where CS is the completion_signatures specialization above. Let C be either set_value_t or set_stopped_t. Then:

    • (7.1) — The expression connect(sndr, rcvr) has type run-loop-opstate<decay_t<decltype((rcvr))>> and is potentially-throwing if and only if (void(sndr), auto(rcvr)) is potentially-throwing.
    • (7.2) — The expression get_completion_scheduler<C>(get_env(sndr)) is potentially-throwing if and only if sndr is potentially-throwing, has type run-loop-scheduler, and compares equal to the run-loop-scheduler instance from which sndr was obtained.