[libcamera-devel] [PATCH v2 1/3] libcamera: base: class: Expose Extensible private data to other classes

[Laurent Pinchart]

On Sun, Jul 11, 2021 at 08:03:57PM +0300, Laurent Pinchart wrote:
> Despite sharing the same name, the private data class created by the
> Extensible design pattern and the C++ private access specifier have
> different goals. The latter specifies class members private to the
> class, while the former stores data not visible to the application.
> 
> There are use cases for accessing the private data class from other
> classes inside libcamera. Make this possible by exposing public _d()
> functions in the class deriving from Extensible. This won't allow access
> to the private data by applications as the definition of the Private
> class isn't visible outside of libcamera.
> 
> The _d() functions need to be defined as template functions to delay
> their evaluation, as the static_cast() operator in the Extensible::_d()
> functions needs the Private class to be fully defined.

This should read

The _d() functions need to be defined as template functions to delay
their evaluation, as the static_cast() operator in the Extensible::_d()
functions needs the Private class to be fully defined. The template
argument is defaulted an ignored, as only its presence is required to
delay evaluation.

> Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> Reviewed-by: Jacopo Mondi <jacopo at jmondi.org>
> Reviewed-by: Umang Jain <umang.jain at ideasonboard.com>
> Reviewed-by: Hirokazu Honda <hiroh at chromium.org>
> ---
>  include/libcamera/base/class.h | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/include/libcamera/base/class.h b/include/libcamera/base/class.h
> index a07dac057331..8212c3d4a5ae 100644
> --- a/include/libcamera/base/class.h
> +++ b/include/libcamera/base/class.h
> @@ -33,14 +33,24 @@ namespace libcamera {
>  #define LIBCAMERA_DECLARE_PRIVATE()					\
>  public:									\
>  	class Private;							\
> -	friend class Private;
> +	friend class Private;						\
> +	template <bool B = true>					\
> +	const Private *_d() const					\
> +	{								\
> +		return Extensible::_d<Private>();			\
> +	}								\
> +	template <bool B = true>					\
> +	Private *_d()							\
> +	{								\
> +		return Extensible::_d<Private>();			\
> +	}
>  
>  #define LIBCAMERA_DECLARE_PUBLIC(klass)					\
>  	friend class klass;						\
>  	using Public = klass;
>  
>  #define LIBCAMERA_D_PTR()						\
> -	_d<Private>();
> +	_d();
>  
>  #define LIBCAMERA_O_PTR()						\
>  	_o<Public>();

-- 
Regards,

Laurent Pinchart