Meta LWG issue: 2025-06 meeting

[StephanTLavavej]

(Previous meta-issue: #5292)

At the June 2025 meeting, the following LWG issues were resolved in the C++ Working Paper.

❔ Not yet analyzed

• Remaining issues:
  • All done! Thanks @frederick-vs-ja for the speedy and thorough analysis! 😻

❌ Not applicable

If an issue requires no action from implementers, we mark it as N/A. Categories:

• Pure wording clarifications with nothing to implement (these can be changes to non-normative text like examples and informative notes, or wording cleanups to normative text that don't impact observable behavior)
  • LWG-4217 Clarify mdspan layout mapping requirements for rank == 0
  • LWG-4224 Philox engines should be freestanding
  • LWG-4247 Header <stdbit.h> is not yet freestanding
• Something that increases the restrictions placed on users, but implementers aren't expected to enforce those restrictions
• Fixes for obviously broken wording, where implementers would have done the right thing anyways
  • LWG-4227 Missing noexcept operator in [exec.when.all]

😸 Already implemented

Sometimes we cite LWG issues in product code comments as we're implementing their proposed resolutions. When the resolutions are officially accepted, we should remove the citations (as the default assumption is that we're implementing what the Standard says). If something is especially subtle, we can convert the citation to mention the relevant Standard section. Sometimes we should add test coverage - e.g. when the Standard begins requiring something that we were already doing but weren't explicitly testing for.

• Already implemented, comments need to be removed, and messages need to cite the Standard
  • LWG-4245 Operators that interact with counted_iterator and default_sentinel_t should be noexcept
    • Remove comments for LWG-4245 Operators that interact with counted_iterator and default_sentinel_t should be noexcept #5582
    • Remove comments for LWG-4245 #5584
• Implemented without comments
  • LWG-4188 ostream::sentry destructor should handle exceptions
  • LWG-4239 flat_map's transparent comparator no longer works for string literals
    • In feature/flat_map, obviously

🩹 Patches an unimplemented feature

• Recorded this LWG issue in the GitHub issue tracking the feature. That way, we'll remember to verify it, but it doesn't represent net new work.
  • P2300R10 std::execution #4768
    • LWG-4198 schedule_from isn't starting the schedule sender if decay-copying results throws
    • LWG-4200 The operation_state concept can be simplified
    • LWG-4201 with-await-transform::await_transform should not use a deduced return type
    • LWG-4202 enable-sender should be a variable template
    • LWG-4203 Constraints on get-state functions are incorrect
    • LWG-4204 Specification of as-sndr2(Sig) in [exec.let] is incomplete
    • LWG-4205 let_[*].transform_env is specified in terms of the let_* sender itself instead of its child
    • LWG-4208 Wording needs to ensure that in connect(sndr, rcvr) that rcvr expression is only evaluated once
    • LWG-4209 default_domain::transform_env should be returning FWD-ENV(env)
  • P1928R15 <simd> #5141
    • LWG-4231 simd::chunk<N> should use simd-size-type instead of size_t
    • LWG-4232 simd::resize does not resize
  • P2846R6 ranges::reserve_hint #5299
    • LWG-4235 cache_latest_view and to_input_view miss reserve_hint
    • LWG-4236 chunk_view::outer-iterator::value_type should provide reserve_hint
  • P0447R28 <hive> #5301
    • LWG-4233 The helper lambda of std::erase for hive should specify return type as bool
    • LWG-4234 Including <hive> doesn't provide std::begin/end

🐞 Not yet implemented

• Filed a GitHub issue labeled LWG Library Working Group issue
  • LWG-4222 expected constructor from a single value missing a constraint
    • LWG-4222 expected constructor from a single value missing a constraint #5622
    • Implement LWG-4222 expected constructor from a single value missing a constraint #5602
  • LWG-4242 ranges::distance does not work with volatile iterators
    • LWG-4242 ranges::distance does not work with volatile iterators #5623
    • Implement LWG-4242 ranges::distance does not work with volatile iterators #5603