[libcamera-devel] [PATCH v2 3/5] provide a default fixed-sized Span constructor

[Laurent Pinchart]

Hi Christian,

Thank you for the patch.

On Tue, Apr 05, 2022 at 01:42:13AM +0100, Christian Rauch via libcamera-devel wrote:
> This allows to construct empty 0-fixed-sized Spans.
> 
> Signed-off-by: Christian Rauch <Rauch.Christian at gmx.de>
> ---
>  include/libcamera/base/span.h | 2 --
>  include/libcamera/controls.h  | 2 +-
>  2 files changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/include/libcamera/base/span.h b/include/libcamera/base/span.h
> index 88d2e3de..bff4c115 100644
> --- a/include/libcamera/base/span.h
> +++ b/include/libcamera/base/span.h
> @@ -105,8 +105,6 @@ public:
> 
>  	static constexpr std::size_t extent = Extent;
> 
> -	template<bool Dependent = false,
> -		 typename = std::enable_if_t<Dependent || Extent == 0>>

The issue here is that the std::span class has this constraint ([1]):

    This overload participates in overload resolution only if
    extent == 0 || extent == std::dynamic_extent.

[1] https://en.cppreference.com/w/cpp/container/span/span

If we drop the constraint here, we will have an issue when switching to
std::span in the future. Is there a way we could achieve the result
you're aiming for without this change ?

>  	constexpr Span() noexcept
>  		: data_(nullptr)
>  	{
> diff --git a/include/libcamera/controls.h b/include/libcamera/controls.h
> index 665bcac1..de8a7770 100644
> --- a/include/libcamera/controls.h
> +++ b/include/libcamera/controls.h
> @@ -167,7 +167,7 @@ public:
> 
>  		using V = typename T::value_type;
>  		const V *value = reinterpret_cast<const V *>(data().data());
> -		return { value, numElements_ };
> +		return T{ value, numElements_ };
>  	}
> 
>  #ifndef __DOXYGEN__

-- 
Regards,

Laurent Pinchart