Meta LWG issue: 2022-02 meeting

[StephanTLavavej]

(Previous meta-issue: #2236)

At the February 2022 virtual plenary meeting, the following LWG issues were resolved in the C++ Working Paper.

❔ Not yet analyzed

❌ 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)
• 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-3607 contiguous_iterator should not be allowed to have custom iter_move and iter_swap behavior
  • LWG-3619 Specification of vformat_to contains ill-formed formatted_size calls

😸 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-3601 common_iterator's postfix-proxy needs indirectly_readable
  • LWG-3616 LWG-3498 seems to miss the non-member swap for basic_syncbuf
• Implemented without comments
  • LWG-3088 forward_list::merge behavior unclear when passed *this
  • LWG-3650 Are std::basic_string's iterator and const_iterator constexpr iterators?
  • LWG-3643 Missing constexpr in std::counted_iterator

🩹 Patches an unimplemented feature

We should record 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.

🐞 Not yet implemented

• Filed a GitHub issue labeled LWG
  • LWG-3471 polymorphic_allocator::allocate does not satisfy Cpp17Allocator requirements (Filed LWG-3471 polymorphic_allocator::allocate does not satisfy Cpp17Allocator requirements #2550)
  • LWG-3525 uses_allocator_construction_args fails to handle types convertible to pair (Filed LWG-3525 uses_allocator_construction_args fails to handle types convertible to pair #2551)
  • LWG-3598 system_category().default_error_condition(0) is underspecified (filed LWG-3598 system_category().default_error_condition(0) is underspecified #2552)
  • LWG-3612 Inconsistent pointer alignment in std::format (filed LWG-3612 Inconsistent pointer alignment in std::format #2553)
  • LWG-3618 Unnecessary iter_move for transform_view::iterator (filed LWG-3618 Unnecessary iter_move for transform_view::iterator #2554)
  • LWG-3648 format should not print bool with 'c' (filed LWG-3648 format should not print bool with 'c' #2555)
  • LWG-3657 std::hash<std::filesystem::path> is not enabled (filed LWG-3657 std::hash<std::filesystem::path> is not enabled #2556)
• PR out for review
  • LWG-3610 iota_view::size sometimes rejects integer-class types (implemented in LWG-3610: iota_view::size sometimes rejects integer-class types #2542)
  • LWG-3621 Remove feature-test macro __cpp_lib_monadic_optional (implemented in LWG-3621 Remove feature-test macro __cpp_lib_monadic_optional #2543)
  • LWG-3632 unique_ptr "Mandates: This constructor is not selected by class template argument deduction" (implemented in "Implement" LWG-3632 by commenting unique_ptr CTAD #2548)
  • LWG-3654 basic_format_context::arg(size_t) should be noexcept (implemented in LWG-3654: basic_format_context::arg(size_t) should be noexcept #2528)
  • LWG-3661 constinit atomic<shared_ptr<T>> a(nullptr); should work (implemented in LWG-3661: constinit atomic<shared_ptr<T>> a(nullptr); should work #2544)
  • LWG-3660 iterator_traits<common_iterator>::pointer should conform to [iterator.traits] (implemented in Implement LWG-3660 for iterator_traits<common_iterator>::pointer #2549)

[fsb4000]

LWG-3643 has already been implemented:

STL/stl/inc/iterator

Lines 1177 to 1181 in bbd5dba

	constexpr decltype(auto) operator++(int) {
	#if _ITERATOR_DEBUG_LEVEL != 0
	_STL_VERIFY(_Length > 0, "counted_iterator increment beyond end of range");
	#endif // _ITERATOR_DEBUG_LEVEL != 0
	--_Length;

[frederick-vs-ja]

Personal analyzation:

❌ Not applicable

• LWG-3607 (only relaxes restrictions for implementations and strengthens restrictions for users)
• LWG-3619 (wording fixes only)
• LWG-3632 (wording fixes; also implemented in an alternative way)

😸 Already implemented

• With comments
  • LWG-3601
  • LWG-3616
• Without comments
  • LWG-3088
  • LWG-3650
  • LWG-3660 the condition whether decltype(a.operator->()) is used seems implemented incorrectly, fix may be needed

🐞 Not yet implemented

• LWG-3471 may be N/A, if no related lifetime-based optimization is available
• LWG-3525
• LWG-3598
• LWG-3610 WIP
• LWG-3612
• LWG-3618
• LWG-3621 WIP
• LWG-3648
• LWG-3657
• LWG-3661 WIP

[CaseyCarter]

Thanks, @frederick-vs-ja! That's a ton of work. I put LWG-3632 under "not implemented" because I think we need a comment to explain why those constructors don't look like they do in the Standard to avoid confusion.

I've pushed a commit into #2549 to cleanup the comments for LWG-3601 and LWG-3616, after which I think we no longer need this tracking issue.