Meta LWG issue: 2023-06 meeting

[frederick-vs-ja]

(Previous meta-issue: #3437)

At the June 2023 meeting, the following LWG issues were resolved in the C++ Working Paper.

❔ Not yet analyzed

(Nothing here!)

❌ 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-3903 span destructor is redundantly noexcept
  • LWG-3905 Type of std::fexcept_t
  • LWG-3915 Redundant paragraph about expression variations
• 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-3885 'op' should be in [zombie.names]
  • LWG-3914 Inconsistent template-head of ranges::enumerate_view
  • LWG-3927 Unclear preconditions for operator[] for sequence containers
  • LWG-3935 template<class X> constexpr complex& operator=(const complex<X>&) has no specification

😸 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-3912 enumerate_view::iterator::operator- should be noexcept
    • Filed Clean up comments for LWG-3912 enumerate_view::iterator::operator- should be noexcept #3780.
  • LWG-3940 std::expected<void, E>::value() also needs E to be copy constructible
    • Filed Clean up comments for LWG-3940 std::expected<void, E>::value() also needs E to be copy constructible #3779.

• Implemented without comments

  • LWG-2994 Needless UB for basic_string and basic_string_view
    For some historical reason, we didn't reject erroneous uses in all modes.
    

    STL/stl/inc/xstring

    Lines 2334 to 2335 in 15aea98

    	static_assert(!_ENFORCE_MATCHING_ALLOCATORS || is_same_v<_Elem, typename _Alloc::value_type>,
    	_MISMATCHED_ALLOCATOR_MESSAGE("basic_string<T, Traits, Allocator>", "T"));

  • LWG-3887 Version macro for allocate_at_least
  • LWG-3938 Cannot use std::expected monadic ops with move-only error_type

🩹 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.

• LWG-3884 flat_foo is missing allocator-extended copy/move constructors
  • Recorded in P0429R9 <flat_map> #2910 and P1222R4 <flat_set> #2912.
• LWG-3894 generator::promise_type::yield_value(ranges::elements_of<Rng, Alloc>) should not be noexcept
  • Recorded in P2502R2 <generator>: Synchronous Coroutine Generator For Ranges #2936.
• LWG-3925 Concept formattable's definition is incorrect
  • Recorded in P2286R8 Formatting Ranges #2919.

🐞 Not yet implemented

• PR out for review
  • LWG-3893 LWG-3661 broke atomic<shared_ptr<T>> a; a = nullptr;
    • PR Implement LWG-3893 LWG-3661 broke atomic<shared_ptr<T>> a; a = nullptr; #3782.
  • LWG-3904 lazy_split_view::outer-iterator's const-converting constructor isn't setting trailing_empty_
    • PR Implement LWG-3904 lazy_split_view::outer-iterator's const-converting constructor isn't setting trailing_empty_ #3781.

[StephanTLavavej]

I fixed a bit of damaged Markdown and recorded the patches to the unimplemented features, so I think we're done processing this meeting's issues in record time - thank you so much! 😻