[Bug c++/39934] Union member incorrectly disallowed

[redi at gcc dot gnu dot org]

------- Comment #8 from redi at gcc dot gnu dot org  2009-11-03 18:10 -------
(In reply to comment #6)
> 
> The ARM comment (as quoted) is clearly wrong: offhand, I can think of
> two other ways of getting an object initialized.  There are probably
> more.
> 
> 1. Casting the offending "const" away.  (Note that struct A is a plain
>    old C type -- data members only.)

It's irrelevant that it has data members only.  Casting away const on an object
declared const is undefined behaviour.

> 2. Copying an existing object.
> 
>    A a (*pa);

Copy construction is dealt with separately from copy assignment, so
has_complex_assign_ref is not relevant in this case.

So the ARM comment may be incorrect, but not due to either of your reasons.

As I said earlier, I'm not sure whether using A in a union causes the
implicitly-declared copy assignment operator to be implicitly defined.  This
issue hinges on that point, not on the points you've been making.

The standard is clear that a copy assignment operator is implicitly-declared.
If it is implicitly defined then that copy assignment operator would be
ill-formed.
So the only question is whether using the type in a union causes it to be
implicitly defined.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39934