[cxx-abi-dev] C++0x POD

[David Vandevoorde]

On Jul 21, 2009, at 6:17 PM, Lawrence Crowl wrote:

> On 7/18/09, David Vandevoorde <daveed at edg.com> wrote:
>> On Jul 17, 2009, at 8:05 AM, Lawrence Crowl wrote:
>
[...]
>>> The C++0x library now requires an O(1) size operator.
>
>> Not yet :-) That will be voted on in a few hours (at the time of
>> the time of this writing).
>
> And that vote passed.  The requirement is now in the working draft.


Indeed.

[...]
>>> Howard Hinnant informs me that Apple plans to not have any
>>> binary compatibility between the two versions of the standard,
>>> except that standard exceptions are binary compatible and hence
>>> can cross from one version to another.
>
>> And certainly every vendor is at liberty to change their library
>> signatures.  However, some vendors also plan to avoid breaking
>> library compatibility if they can and with the current standard
>> revision, that is entirely possible (because they already have
>> an O(1) std::list::size() and a non-reference-counted std::string).
>
>> Even those vendors that will have to break compatibility may
>> provide binary compatibility options with e.g. inline namespaces.
>
>> In either case, I am not willing to foil such goals by changing
>> the underlying ABI.
>
> First, let me note that I argued strongly in favor of taking some
> position on binary compatiblity, but was unable to get the committee
> to adopt a policy.  As a result, we have inconsistent expectations
> on compatiblity.
>
> Second, my concern is that we probably will not have effective
> binary compatibility anyway, and not taking advantage of that
> incompatibility has real performance costs.


Maybe.  However, although concepts are out of C++0x, they are still  
"on the horizon".  Concepts change the library-ABI very drastically.   
I suspect that several vendors will therefore consider delaying other  
ABI-breaking transitions to coincide with the implementation of  
concepts (in whatever form they reappear).  (That's also why I voted  
against the O(1) size change: I find it unwise to break the library  
ABI piece-by-piece instead of wholesale at distant release points.)

	Daveed