Skip to content

Implement LWG-3436 std::construct_at should support arrays - #5920

Merged
Stephan T. Lavavej (StephanTLavavej) merged 12 commits into
microsoft:mainfrom
frederick-vs-ja:lwg-3436
Feb 2, 2026
Merged

Implement LWG-3436 std::construct_at should support arrays#5920
Stephan T. Lavavej (StephanTLavavej) merged 12 commits into
microsoft:mainfrom
frederick-vs-ja:lwg-3436

Conversation

@frederick-vs-ja

@frederick-vs-ja A. Jiang (frederick-vs-ja) commented Dec 1, 2025 •
edited
Loading

Copy link
Copy Markdown
Contributor

Fixes #5110.

Currently, all tested compilers (MSVC, Clang, and EDG) need some workaround for constant evaluation.

  • MSVC is blocked by lack of [[msvc::constexpr]] of the involved operator new[] in VCRuntime.
    • I'm attempting to introduce a new operator new[] overload, which is sufficiently constrained to avoid affecting overload resolution, as a workaround. However, it doesn't work for non-trivially destructible element types, because MSVC will require additional space to record the number of class objects to destroy.
  • Clang crashes when directly using the final resolution of LWG-3436.
    • The old proposed resolution is used as a workaround.
  • EDG simply can't accept the final resolution in constant evaluation.
    • The old proposed resolution is used as a workaround.
  • Also, EDG doesn't correctly recognize the allocated element type of std::allocator<T[N]>::allocate in constant evaluation.
    • Workaround is unknown, so such case isn't made supported for EDG yet.
  • Also, EDG crashes in some cases in constant evaluation.
    • Workaround is unknown, so such case isn't made supported for EDG yet.

Reported issues:
@frederick-vs-ja
A. Jiang (frederick-vs-ja) requested a review from a team as a code owner December 1, 2025 01:33
@github-project-automation github-project-automation Bot moved this to Initial Review in STL Code Reviews Dec 1, 2025
@StephanTLavavej Stephan T. Lavavej (StephanTLavavej) added the LWG Library Working Group issue label Dec 1, 2025
StephanTLavavej
Stephan T. Lavavej (StephanTLavavej) reviewed Dec 7, 2025
View reviewed changes
Comment thread stl/inc/xutility Outdated
Comment thread tests/std/tests/P0784R7_library_support_for_more_constexpr_containers/test.cpp Outdated
Comment thread tests/std/tests/P1004R2_constexpr_vector/test.cpp Outdated
Comment thread tests/std/tests/P1004R2_constexpr_vector/test.cpp Outdated
Comment thread tests/std/tests/P1004R2_constexpr_vector/test.cpp Outdated
StephanTLavavej
Stephan T. Lavavej (StephanTLavavej) reviewed Jan 30, 2026
View reviewed changes
Comment thread tests/std/tests/P0784R7_library_support_for_more_constexpr_containers/test.cpp Outdated
Comment thread tests/std/tests/P0784R7_library_support_for_more_constexpr_containers/test.cpp Outdated
Comment thread tests/std/tests/P1004R2_constexpr_vector/test.cpp Outdated
@StephanTLavavej

Stephan T. Lavavej (StephanTLavavej) commented Jan 30, 2026

Copy link
Copy Markdown
Member

Thanks for reporting all of these compiler bugs, I really appreciate it! 😻
@StephanTLavavej Stephan T. Lavavej (StephanTLavavej) moved this from Initial Review to Ready To Merge in STL Code Reviews Jan 30, 2026
@StephanTLavavej Stephan T. Lavavej (StephanTLavavej) moved this from Ready To Merge to Merging in STL Code Reviews Jan 30, 2026
@StephanTLavavej

Stephan T. Lavavej (StephanTLavavej) commented Jan 30, 2026

Copy link
Copy Markdown
Member

I'm mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed.
@StephanTLavavej
Stephan T. Lavavej (StephanTLavavej) merged commit 7f083b9 into microsoft:main Feb 2, 2026
45 checks passed
@github-project-automation github-project-automation Bot moved this from Merging to Done in STL Code Reviews Feb 2, 2026
@StephanTLavavej

Stephan T. Lavavej (StephanTLavavej) commented Feb 2, 2026

Copy link
Copy Markdown
Member

⚙️ 😻 🎁
Closed
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment

Labels

LWG Library Working Group issue

2 participants

@frederick-vs-ja @StephanTLavavej