[PATCH v1 3/3] libcamera: controls: Implement `swap()`

[Kieran Bingham]

Quoting Barnabás Pőcze (2025-04-17 12:35:39)
> Implement both free and member function `swap()` for `ControlValue`.
> The general `std::swap()` swaps two values by combining a move construction
> and two move assignments, but for `ControlValue` a simpler implementation
> can be provided by just swapping the members.
> 
> Signed-off-by: Barnabás Pőcze <barnabas.pocze at ideasonboard.com>
> ---
>  include/libcamera/controls.h | 24 ++++++++++++++++++++++++
>  src/libcamera/controls.cpp   | 15 +++++++++++++++
>  2 files changed, 39 insertions(+)
> 
> diff --git a/include/libcamera/controls.h b/include/libcamera/controls.h
> index 86245e7a9..27b314dbc 100644
> --- a/include/libcamera/controls.h
> +++ b/include/libcamera/controls.h
> @@ -261,6 +261,30 @@ public:
>         void reserve(ControlType type, bool isArray = false,
>                      std::size_t numElements = 1);
>  
> +       void swap(ControlValue &other) noexcept
> +       {
> +               {
> +                       auto tmp = type_;
> +                       type_ = other.type_;
> +                       other.type_ = tmp;
> +               }

I fear I'm missing something obvious ... why are type_ and numElements_
not items that can simply be swapped with std::swap() ?

Is it because of the need to use auto on the type? or something else?

Should this implementation go into controls.cpp ? or is it
required/better inline in the header ?

> +
> +               std::swap(isArray_, other.isArray_);
> +
> +               {
> +                       auto tmp = numElements_;
> +                       numElements_ = other.numElements_;
> +                       other.numElements_ = tmp;
> +               }
> +
> +               std::swap(storage_, other.storage_);
> +       }
> +
> +       friend void swap(ControlValue &a, ControlValue &b) noexcept
> +       {
> +               a.swap(b);
> +       }
> +
>  private:
>         ControlType type_ : 8;
>         bool isArray_;
> diff --git a/src/libcamera/controls.cpp b/src/libcamera/controls.cpp
> index 885287e71..c1ff60f39 100644
> --- a/src/libcamera/controls.cpp
> +++ b/src/libcamera/controls.cpp
> @@ -411,6 +411,21 @@ void ControlValue::reserve(ControlType type, bool isArray, std::size_t numElemen
>                 storage_.external = new uint8_t[newSize];
>  }
>  
> +/**
> + * \fn ControlValue::swap(ControlValue &other) noexcept
> + * \brief Swap two control values
> + *
> + * This function swaps the contained value of \a this with that of \a other.
> + */
> +
> +/**
> + * \fn ControlValue::swap(ControlValue &a, ControlValue &b) noexcept
> + * \brief Swap two control values
> + *
> + * This function swaps the contained value of \a a with that of \a b.
> + * \sa ControlValue::swap()
> + */
> +
>  /**
>   * \class ControlId
>   * \brief Control static metadata
> -- 
> 2.49.0
>