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CWG3035 [class.union.anon] Are lambda expressions disallowed in anonymous unions? #706
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I think the wording is fairly clear on this, although it is surprising that IILEs wouldn't be okay.
I doubt that the current behavior is intentional, and maybe a better approach would be to ask EWG to exclude closure types, effectively standardizing what Clang, GCC, and MSVC already do. If we don't do that, the resolution looks correct.
- changed the title
[-][class.union.anon] Are lambda expressions disallowed in anonymous unions?[/-][+]CWG3035 [class.union.anon] Are lambda expressions disallowed in anonymous unions?[/+]on Jul 26, 2025 We can probably fix cplusplus/draft#4938 at the same time while we are at it.
We can probably fix cplusplus/draft#4938 at the same time while we are at it.
@hubert-reinterpretcast Do you mean something like this?
Nested types, including closure types (7.5.6.2 [expr.prim.lambda.closure]) and anonymous unions, and functions other than implicitly-declared special member functions shall not be declared within an anonymous union....
@hubert-reinterpretcast Do you mean something like this?
Nested types, including closure types (7.5.6.2 [expr.prim.lambda.closure]) and anonymous unions, and functions other than implicitly-declared special member functions shall not be declared within an anonymous union....
Yes. Although, with the discussion happening around https://cplusplus.github.io/CWG/issues/3130.html, it seems we should probably hold off on doing anything about implicitly-declared special member functions here.
Full name of submitter (unless configured in github; will be published with the issue): Hubert Tong
Reference (section label): class.union.anon
Link to reflector thread (if any): N/A
Issue description:
https://eel.is/c++draft/class.union.anon#1.sentence-3 says:
A lambda expression declares a closure type (https://eel.is/c++draft/expr.prim.lambda#closure-2).
Does that mean that lambda expressions are disallowed in anonymous unions?
Only EDG generates a diagnostic for https://godbolt.org/z/xf96EbKTn:
Suggested resolution: