[RFC] C++1x breaking the ABI in one more place :(

[Ian Lance Taylor]

Mark Mitchell <mark@codesourcery.com> writes:

> Joe Buck wrote:
>
>> But this is a kind of breakage that might be acceptable to fix an
>> otherwise broken library (though users should be warned about it),
>> especially in cases where we wouldn't expect this kind of use.
>
> I agree -- but not without a bump in the .so number.  It is a serious
> binary incompatibility, unless you can convince yourself that nobody
> derived from this class.

The vtables in libstdc++ have symbol versions.  Therefore it is
possible in principle to keep the old vtable at the old symbol version
(GLIBCXX_3.4) and provide the new vtable at the new version.

Ian