On Wed, Jul 29, 2020 at 07:21:46PM -0400, Jason Merrill via Gcc-patches wrote:
> On 7/20/20 7:28 PM, Marek Polacek wrote:
> > P1975R0 tweaks the static_cast wording: it says that "An expression e can be
> > explicitly converted to a type T if [...] T is an aggregate type having a
> > first
> > element x and there is an implicit conversion sequence from e to the type of
> > x." This already works for classes, e.g.:
> >
> > struct Aggr { int x; int y; };
> > Aggr a = static_cast<Aggr>(1);
> >
> > albeit I noticed a -Wmissing-field-initializer warning which is unlikely to
> > be
> > helpful in this context, as there's nothing like static_cast<Aggr>(1, 2)
> > to quash that warning.
>
> You could write Aggr{1,2} instead?
>
> This warning could be helpful if they didn't realize that what they were
> writing is initializing one element of an aggregate.
Ok, I can drop it. Though explicit cast usually suppress warnings like that.
> > However, the proposal also mentions "If T is ``array of unknown bound of
> > U'',
> > this direct-initialization defines the type of the expression as U[1]" which
> > suggest that this should work for arrays (they're aggregates too, after
> > all).
> > Ville, can you confirm that these
> >
> > int (&&r)[3] = static_cast<int[3]>(42);
> > int (&&r2)[1] = static_cast<int[]>(42);
> >
> > are supposed to work now? There's no {} variant to check. Thanks.
>
> I'll review the discussion of this later.
It's become clear that the array cases are supposed to work, so I think
let's drop this patch and I'll post a new patch when I get the array cases
working.
Thanks,
Marek
