[PATCH] D62988: Add an attribute to allow fields of non-trivial types in C unions

[Richard Smith - zygoloid via Phabricator via cfe-commits]

rsmith added a comment.

How do you write correct (non-leaking, non-double-freeing, non-releasing-invalid-pointers) code with this attribute? For example, suppose I have a `__strong` union member: does storing to it release the old value (which might be a different union member)? If so, how do you work around that? https://clang.llvm.org/docs/AutomaticReferenceCounting.html#ownership-qualified-fields-of-structs-and-unions should be updated to say what happens. If manual reference counting code is required to make any use of this feature correct (which seems superficially likely), is this a better programming model than `__unsafe_unretained`?

Unions with non-trivial members are only permitted in C++11 onwards; should we allow the attribute in C++98 mode? But more than that, unions with non-trivial members require user-provided special members in C++11 onwards, meaning that a union using this attribute in C would have a different calling convention than the "natural" equivalent in C++. So I'm also wondering if we should allow this in all language modes.


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  rC Clang

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  https://reviews.llvm.org/D62988/new/

https://reviews.llvm.org/D62988