[PATCH v3 04/16] libcamera: vector: Add a Span based constructor

[Kieran Bingham]

Quoting Stefan Klug (2025-04-03 16:49:09)
> When one wants to create a Vector from existing data, currently the only
> way is via std::array. Add a Span based constructor to allow creation
> from std::vectors and alike.
> 
> While at it, replace the manual loop with std::copy.
> 
> Signed-off-by: Stefan Klug <stefan.klug at ideasonboard.com>
> Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> 

Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>

> ---
> 
> Changes in v2:
> - Added this patch
> 
> Changes in v3:
> - Improved commit message
> - Added constexpr to the contructor
> - Pass Span by value
> - Removed initializer of data_ member which was only needed for the
>   default constructor to be actually constexpr. But Vector is not used
> as constexpr anywhere, so we can leave that as is (This will fix itself
> with C++20).
> ---
>  include/libcamera/internal/vector.h | 8 ++++++--
>  src/libcamera/vector.cpp            | 8 ++++++++
>  2 files changed, 14 insertions(+), 2 deletions(-)
> 
> diff --git a/include/libcamera/internal/vector.h b/include/libcamera/internal/vector.h
> index a67a09474204..4e9ef1ee6853 100644
> --- a/include/libcamera/internal/vector.h
> +++ b/include/libcamera/internal/vector.h
> @@ -42,8 +42,12 @@ public:
>  
>         constexpr Vector(const std::array<T, Rows> &data)
>         {
> -               for (unsigned int i = 0; i < Rows; i++)
> -                       data_[i] = data[i];
> +               std::copy(data.begin(), data.end(), data_.begin());
> +       }
> +
> +       constexpr Vector(const Span<const T, Rows> data)
> +       {
> +               std::copy(data.begin(), data.end(), data_.begin());
>         }
>  
>         const T &operator[](size_t i) const
> diff --git a/src/libcamera/vector.cpp b/src/libcamera/vector.cpp
> index 85ca2208245a..5567d5b8defb 100644
> --- a/src/libcamera/vector.cpp
> +++ b/src/libcamera/vector.cpp
> @@ -44,6 +44,14 @@ LOG_DEFINE_CATEGORY(Vector)
>   * The size of \a data must be equal to the dimension size Rows of the vector.
>   */
>  
> +/**
> + * \fn Vector::Vector(const Span<const T, Rows> data)
> + * \brief Construct vector from supplied data
> + * \param data Data from which to construct a vector
> + *
> + * The size of \a data must be equal to the dimension size Rows of the vector.
> + */
> +
>  /**
>   * \fn T Vector::operator[](size_t i) const
>   * \brief Index to an element in the vector
> -- 
> 2.43.0
>