[PATCH v1 2/3] libcamera: controls: Implement move ctor/assignment

[Kieran Bingham]

Quoting Barnabás Pőcze (2025-04-17 12:35:38)
> Implement a move constructor and move assignment operator for `ControlValue`.
> The `ControlValue` type already has an "empty" state that it used when
> creating a default constructed `ControlValue`, so have the moved-from
> instance return to that state after move construction/assignment.
> 
> This is useful, for example, for `std::vector` as most implementations will
> use the copy constructor when reallocating if no nothrow move constructor
> is available. Having a nothrow move constructor avoids the extra copies.
> It is also useful when using temporaries of `ControlValue` with other
> containers such as `std::optional`, and it also makes `ControlInfo`
> "cheaply" move constructible/assignable.
> 
> Signed-off-by: Barnabás Pőcze <barnabas.pocze at ideasonboard.com>
> ---
>  include/libcamera/controls.h | 28 ++++++++++++++++++++++++++++
>  src/libcamera/controls.cpp   | 17 +++++++++++++++++
>  2 files changed, 45 insertions(+)
> 
> diff --git a/include/libcamera/controls.h b/include/libcamera/controls.h
> index 1dc6ccffa..86245e7a9 100644
> --- a/include/libcamera/controls.h
> +++ b/include/libcamera/controls.h
> @@ -14,6 +14,7 @@
>  #include <stdint.h>
>  #include <string>
>  #include <unordered_map>
> +#include <utility>
>  #include <vector>
>  
>  #include <libcamera/base/class.h>
> @@ -165,6 +166,33 @@ public:
>         ControlValue(const ControlValue &other);
>         ControlValue &operator=(const ControlValue &other);
>  
> +       ControlValue(ControlValue &&other) noexcept
> +               : type_(other.type_),
> +                 isArray_(std::exchange(other.isArray_, false)),
> +                 numElements_(other.numElements_),
> +                 storage_(std::exchange(other.storage_, {}))
> +       {
> +               other.type_ = ControlTypeNone;
> +               other.numElements_ = 0;
> +       }
> +
> +       ControlValue &operator=(ControlValue &&other) noexcept
> +       {
> +               if (this != &other) {
> +                       release();
> +

If we invert this we can lower the indent:
		if (this == &other)
			return *this;

		release();
		type_ = other.type_;
		...

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

> +                       type_ = other.type_;
> +                       isArray_ = std::exchange(other.isArray_, false);
> +                       numElements_ = other.numElements_;
> +                       storage_ = std::exchange(other.storage_, {});
> +
> +                       other.type_ = ControlTypeNone;
> +                       other.numElements_ = 0;
> +               }
> +
> +               return *this;
> +       }
> +
>         ControlType type() const { return type_; }
>         bool isNone() const { return type_ == ControlTypeNone; }
>         bool isArray() const { return isArray_; }
> diff --git a/src/libcamera/controls.cpp b/src/libcamera/controls.cpp
> index d384e1ef7..885287e71 100644
> --- a/src/libcamera/controls.cpp
> +++ b/src/libcamera/controls.cpp
> @@ -155,6 +155,23 @@ ControlValue &ControlValue::operator=(const ControlValue &other)
>         return *this;
>  }
>  
> +/**
> + * \fn ControlValue::ControlValue(ControlValue &&other) noexcept
> + * \brief Move constructor for ControlValue
> + * \param[in] other The ControlValue object to move from
> + *
> + * Move constructs a ControlValue instance from \a other. After this opreation
> + * \a other will be in the same state as a default constructed ControlValue instance.
> + */
> +
> +/**
> + * \fn ControlValue &ControlValue::operator=(ControlValue &&other) noexcept
> + * \brief Move assignment operator for ControlValue
> + * \param[in] other The ControlValue object to move from
> + *
> + * \sa ControlValue::ControlValue(ControlValue &&other)
> + */
> +
>  /**
>   * \fn ControlValue::type()
>   * \brief Retrieve the data type of the value
> -- 
> 2.49.0
>