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[std-proposals] `mdspan` CTAD specialization for `integral_constant`?

From: Hewill Kang <hewillk_at_[hidden]>
Date: Thu, 5 Oct 2023 15:21:19 +0800
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]
<https://eel.is/c++draft/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

Received on 2023-10-05 07:21:31