Am Mittwoch, dem 14.08.2024 um 16:12 +0200 schrieb Alejandro Colomar:
> Hi Martin,
>
> On Wed, Aug 14, 2024 at 03:50:00PM GMT, Martin Uecker wrote:
> > An operator that returns an array with all dimensions of a multi-dimensional
> > array would make a a lot of sense to me.
> >
> >
> > double array[4][3][2];
> >
> > // array_dims(array) = (constexpr size_t[3]){ 4, 3, 2 }
>
> And what if array[4][n][2]? No constexpr anymore, which is bad.
> >
> > int dim1 = (array_dims(array))[0]
> > int dim2 = (array_dims(array))[1]
> > int dim3 = (array_dims(array))[2]
> >
> > You can then implement lengthof in terms of this operator:
> >
> > #define lengthof(x) (array_dims(array)[0])
>
> Not really. This implementation would result in less constant
> expressions that my proposal. That's detrimental for diagnostics and
> usability.
Yes, this would be a downside when implementing lengthof
in this way.
>
> And the fundamental operator would be very complex, to allow users
> implementing simpler wrappers. I think the fundamental operators should
> be as simple as possible, in the spirit of C, and let users build on top
> of those basic tools.
>
> This reminds me of the 'static' specifier for array parameters, which is
> conflated with two meanings: nonnull and length. I'd rather have a way
> to specify nullness, and another one to specify length, and let users
> compose them.
>
> At first glance I oppose this array_dims operator.
Opinionated as usual ;-)
> > and you can obtain the rank by applying lengthof to the array:
> >
> > #define rank(x) lengthof(array_dims(x))
>
> I'm curious to see what kind of code would be enabled by a rank()
> operator in C that we can't write at the moment.
There seems to be no generic way to get all dimensions from
a multi-dimensional array of arbitrary rank.
Martin
>
> > If the array is constexpr for regular arrays and array
> > indexing returns a constant again for constexpr arrays, this
> > would all work out.
> >
> > Martin
>
> Have a lovely day!
> Alex
>
--
Univ.-Prof. Dr. rer. nat. Martin Uecker
Graz University of Technology
Institute of Biomedical Imaging
