[PATCH v1] libcamera: base: bound_method: Simplify `invokePack()`

[Laurent Pinchart]

Hi Barnabás,

Thank you for the patch.

On Mon, Mar 31, 2025 at 06:03:01PM +0200, Barnabás Pőcze wrote:
> Use `if constexpr` instead of SFINAE to handle return values of type `void`.
> 
> Signed-off-by: Barnabás Pőcze <barnabas.pocze at ideasonboard.com>
> ---
>  include/libcamera/base/bound_method.h | 17 ++++++-----------
>  1 file changed, 6 insertions(+), 11 deletions(-)
> 
> diff --git a/include/libcamera/base/bound_method.h b/include/libcamera/base/bound_method.h
> index dd3488eeb..aad75c02a 100644
> --- a/include/libcamera/base/bound_method.h
> +++ b/include/libcamera/base/bound_method.h
> @@ -98,21 +98,16 @@ public:
>  	using PackType = BoundMethodPack<R, Args...>;
>  
>  private:
> -	template<std::size_t... I, typename T = R>
> -	std::enable_if_t<!std::is_void<T>::value, void>
> +	template<std::size_t... I>
> +	void
>  	invokePack(BoundMethodPackBase *pack, std::index_sequence<I...>)

You can write

	template<std::size_t... I>
	void invokePack(BoundMethodPackBase *pack, std::index_sequence<I...>)

>  	{
>  		PackType *args = static_cast<PackType *>(pack);
> -		args->ret_ = invoke(std::get<I>(args->args_)...);
> -	}
>  
> -	template<std::size_t... I, typename T = R>
> -	std::enable_if_t<std::is_void<T>::value, void>
> -	invokePack(BoundMethodPackBase *pack, std::index_sequence<I...>)
> -	{
> -		/* args is effectively unused when the sequence I is empty. */
> -		PackType *args [[gnu::unused]] = static_cast<PackType *>(pack);
> -		invoke(std::get<I>(args->args_)...);
> +		if constexpr (!std::is_void_v<R>)
> +			args->ret_ = invoke(std::get<I>(args->args_)...);
> +		else
> +			invoke(std::get<I>(args->args_)...);

I'm surprised that this works. I didn't know that within a templated
entity the discarded statement is not instantiated. It's interesting.

Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>

>  	}
>  
>  public:

-- 
Regards,

Laurent Pinchart