Re: libstdc++ PATCH to add abi tag to complex::real/imag

[Jason Merrill <jason at redhat dot com>]

On 11/11/2012 06:55 AM, Jonathan Wakely wrote:
> For std::list I assume we want the attribute on the type itself, not
> just member functions, since its size changes.

Yes.  Note that I believe for the list and string changes we want to 
change the default ABI for C++98 and C++11, not just C++11.  And provide 
a way for users to select the old ABI if they need to pass string/list 
objects to and from previously compiled code.

> As well as the existing incompatibilities, I need to add a new virtual
> function to support returning future_status::deferred from
> std::future::wait_{for,until}.  Is it appropriate to use the same
> "cxx11" tag for that too, even though the existing implementation is
> also "cxx11" because the type wasn't in C++98?   Or do we want to use
> a different tag, such as "cxx11v2" or just "v2"?

If this is a C++11-only class, then I don't think we need a tag at all. 
 I don't think we've been trying to maintain binary compatibility 
between major releases for C++11 code.  The goal of all of this is to 
allow old C++98 code to coexist in the same running program with new 
C++11 code so long as they aren't trying to use the same string/list 
objects.

Jason