wt., 17 paź 2023 o 05:41 Hewill Kang via Std-Proposals
<std-proposals_at_[hidden]> napisał(a):
>
> Hi fellow experts,
>
> I wrote a paper based on this thread:
>
> https://htmlpreview.github.io/?https://github.com/hewillk/mdspan-ctad/blob/main/mdspan-ctad.html
>
> It is still in the draft stage so there may be parts that need to be considered. Any comments are welcome.
>
> Hewill
>
>
> Hewill Kang <hewillk_at_[hidden]> 於 2023年10月5日 週四 下午3:21寫道：
>>
>> Hi fellow experts
>>
>> I initially thought that
>>
>> mdspan ms(ptr, integral_constant<size_t, 2>{}, integral_constant<size_t, 6>{});
>>
>> would be deduced into mdspan<int, extents<size_t, 2, 6>>. However, as the current wording ([mdspan.mdspan.overview]), it is just mdspan<int, extents<size_t, dynamic_extent, dynamic_extent>>
>>
>> template<class ElementType, class... Integrals>
>> requires((is_convertible_v<Integrals, size_t> && ...) && sizeof...(Integrals) > 0)
>> explicit mdspan(ElementType*, Integrals...)
>> -> mdspan<ElementType, dextents<size_t, sizeof...(Integrals)>>;
>>
>> I wonder, is it a more appropriate choice to set the corresponding extents's static values based on whether Integrals... is integral_constant? For example
>>
>> mdspan ms(ptr, integral_constant<size_t, 2>{},
>> integral_constant<size_t, 3>{},
>> 4,
>> integral_constant<size_t, 5>{});
>>
>> which will be deduced as mdspan<int, extents<size_t, 2, 3, dynamic_extent, 5>>.
>>
>> What do you guys think? Could this be considered an improvement?
>>
>> Hewill

Would be better that instead of type alias use template variable?
Then code will look more clean:

```
//paper version:
mdspan ms(p, integral_c<3>{}, 42, integral_c<5>{});


//bit streamlined version:
template<auto I>
std::integral_constant<decltype(I), I> integral_c = {};

mdspan ms(p, integral_c<3>, 42, integral_c<5>);
```
probably name could be even shortened like:

```
std::mdspan ms(p, std::c<3>, 42, std::c<5>);
```

another option is user defined literals but there
is problem for good suffix as many are already
used or could conflict with hex numbers (like suffix `c`).


>
> --
> Std-Proposals mailing list
> Std-Proposals_at_[hidden]
> https://lists.isocpp.org/mailman/listinfo.cgi/std-proposals