On Sun, 2025-06-08 at 21:33 +0100, Jonathan Wakely wrote:
>
>
> On Sun, 8 Jun 2025, 09:46 Avi Kivity, <avi_at_[hidden]> wrote:
> > On Sat, 2025-06-07 at 22:25 +0100, Jonathan Wakely wrote:
> > >
> > >
> > > On Sat, 7 Jun 2025, 22:20 Avi Kivity via Std-Proposals,
> > > <std-proposals_at_[hidden]> wrote:
> > > > On Sat, 2025-06-07 at 21:57 +0300, Ville Voutilainen via Std-
> > > > Proposals wrote:
> > > > > On Sat, 7 Jun 2025 at 21:44, Robin Savonen Söderholm via Std-
> > > > > Proposals
> > > > > <std-proposals_at_[hidden]> wrote:
> > > > > >
> > > > > > You can easily implement your own version of optional that
> > > > > > does exactly that (it would even be a simpler class to
> > > > > > implement, although not to use). The question then is why?
> > > > > > If you somehow think that you would gain performance out of
> > > > > > it, then my suggestion is: implement this type of optional
> > > > > > and show both a benchmark where it makes a significant
> > > > > > difference and tell us the use case where this performance
> > > > > > gain can be leveraged.
> > > > > >
> > > > > > My 2 c.
> > > > >
> > > > > That's easy. The hard part is figuring out how to deploy such
> > > > > a type
> > > > > with the same name as its previous version that didn't use
> > > > > the dummy value protocol. It's a behavioral ABI break without
> > > > > any
> > > > > layout ABI break.
> > > > >
> > > >
> > > >
> > > >
> > > > This was solved already when std::string changed its ABI. The
> > > > compilers shipped the standard library compiled in both modes
> > > > for a while, then dropped the old mode.
> > >
> > > We didn't drop it, both modes are still supported (by a single
> > > binary) and in use today, and it took a year of my life and I
> > > don't want to do it again :-)
> > >
> > > And it still has costs today for every change to std::string (as
> > > we have to decide whether to implement the new stuff for the old
> > > mode too).
> > >
> >
> >
> >
> > Do people use the old string ABI?
>
> Yes, even with the very latest GCC releases, and not just because
> they're stuck on an ancient Linux distro.
>
>

Amazing. I guess they're stuck with third-party object files that
cannot be updated.