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

[Richard Guenther <rguenther@suse.de>]

On Fri, 3 Dec 2010, Jason Merrill 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.

You have to handle similar situations with allocated storage and
arrays of chars anyway, so I don't think unions should
complicate anything.

Richard.