> On Dec 16, 2017, at 9:08 AM, David Zarzycki via swift-dev
> <swift-dev@swift.org> wrote:
>
> Hello,
>
> I’m trying to improve SILNode memory layout density by adopting the AST
> bitfield macros. Unfortunately, multiple inheritance doesn’t seem to get
> along with anonymous/unnamed unions. Here is a distillation of the problem:
>
> class B {
> protected:
> int i;
> union { int j; };
> };
>
> class X : public B { };
> class Y : public B { };
>
> class Z : public X, public Y {
> int a() { return X::i; } // works
> int b() { return X::j; } // fails
> };
>
> Is this expected C++ behavior? I can certainly workaround this by naming the
> unnamed union, but before I do, I thought that I should check here first.
This seems like a bug; anonymous unions are just supposed to inject their
member names into the containing scope as if there was an ordinary member
there, and the explicit scope-qualification should resolve which subobject is
meant for such injected names the same it resolves them for ordinary fields.
But if it's a bug in all existing clangs, it's a bug we're going to have to
work around.
John.
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