On Wed, 12 Aug 2020 at 19:50, Florian Weimer via Liaison
<liaison_at_[hidden]> wrote:
>
> I tried to compile a bunch of C software with a C++ compiler, and
> designated initializers pose a compatibility problem, even with a
> compiler that implements P0329R4.
>
> Would it be possible to lift the ordering constraint? No such
> constraint exists for mem-initializers in constructors, which have the
> same issue regarding destruction order.
>
> The reason I'm asking for this is that historically, C-related
> standard such as POSIX have not specified the order of struct members,
> only that certain types must have certain members. This means that
> there is no single portable order for designated initializers.
>
> The other issue I encountered is use of nested designators. I'm not
> sure if theire use is actually rare.
>
> I'm Cc:ing the C/C++ liaison list, in case others want to chime in.

There's a forum discussion thread about this here:
https://groups.google.com/a/isocpp.org/g/std-proposals/c/FztFJLqEFwY/m/pANgM0hJAAAJ?pli=1

P0329R0 discusses this as a matter that was explicitly considered by
the authors. It was discussed
at length in EWG in the Oulu meeting in 2016. For those who can access
it, the discussion
notes are at https://wiki.edg.com/bin/view/Wg21oulu/P0329R0.

(Just for some background information; I'm not suggesting any value judgement.)

The usual advice applies. To change this, we need a proposal with
well-thought-out rationale, with
a strong recommendation that that rationale should include an
explanation why the points made
in the paper and in the aforementioned discussion are overshadowed by
the benefits of the change.
And since it's an incompatible change to a facility that's been there
for two C++ standards very-soon,
prepare to make the rationale even more convincing.

Oh, would it be possible to lift the ordering requirement? Maybe. My
guesstimate is that that's an uphill
battle.