[PATCH, PR 45934 4/6] Dynamic type change detection

[Gabriel Dos Reis]

On Fri, Dec 3, 2010 at 10:07 AM, Jason Merrill <jason@redhat.com> wrote:
> On 12/03/2010 08:45 AM, Martin Jambor wrote:
>>
>> On Thu, Dec 02, 2010 at 06:25:28PM -0500, Jason Merrill wrote:
>>>
>>> On 12/01/2010 03:16 PM, Martin Jambor wrote:
>>>>
>>>> and there are no unions of non-POD types
>>>
>>> This is actually no longer true in C++0x.
>>
>> OK... but from what I have googled I understand that types with
>> virtual functions are still explicitly not allowed to be fields of
>> a union, right?
>
> They are allowed now. 9.5/4 of N3126:
>
> [ Example: Consider an object u of a union type U having non-static data
> members m of type M and n of type N. If M has a non-trivial destructor and N
> has a non-trivial constructor (for instance, if they declare or inherit
> virtual functions), the active member of u can be safely switched from m to
> n using the destructor and placement new operator as follows:
>  u.m.~M();
>  new (&u.n) N;
> -- end example ]
>
> I wouldn't worry about this for now, though.  I'll add it to the pile of
> union language issues.

Are you anticipating banning them?
I would not think they pose any problem -- copy and assignment
has to be user provided anyway, and assignment to a non-POD
data can be done only to the active member (since it is a
member function call)

-- Gaby