[libcamera-devel] [PATCH/RFC 3/3] v4l2: Replace manual loop counters with utils::enumerate()

[Laurent Pinchart]

Hi Kieran,

On Tue, May 11, 2021 at 11:05:43AM +0100, Kieran Bingham wrote:
> On 23/04/2021 03:09, Laurent Pinchart wrote:
> > Use the newly introduced utils::enumerate() to replace manual loop
> > counters. A local variable is needed, as utils::enumerate() requires an
> > lvalue reference.
> > 
> > Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> > ---
> >  src/v4l2/v4l2_compat_manager.cpp | 18 +++++++++---------
> >  1 file changed, 9 insertions(+), 9 deletions(-)
> > 
> > diff --git a/src/v4l2/v4l2_compat_manager.cpp b/src/v4l2/v4l2_compat_manager.cpp
> > index 90c0f0121a32..bf5bf8e3223d 100644
> > --- a/src/v4l2/v4l2_compat_manager.cpp
> > +++ b/src/v4l2/v4l2_compat_manager.cpp
> > @@ -23,6 +23,7 @@
> >  #include <libcamera/camera_manager.h>
> >  
> >  #include "libcamera/internal/log.h"
> > +#include "libcamera/internal/utils.h"
> >  
> >  #include "v4l2_camera_file.h"
> >  
> > @@ -81,11 +82,11 @@ int V4L2CompatManager::start()
> >  	 * For each Camera registered in the system, a V4L2CameraProxy gets
> >  	 * created here to wrap a camera device.
> >  	 */
> > -	unsigned int index = 0;
> > -	for (auto &camera : cm_->cameras()) {
> > -		V4L2CameraProxy *proxy = new V4L2CameraProxy(index, camera);
> > +	auto cameras = cm_->cameras();
> > +	for (const auto camera : utils::enumerate(cameras)) {
> 
> Is it possible to used named scopes here like:
> 
>     for (const auto [index, camera] : utils::enumerate(cameras)) {
>         V4L2CameraProxy *proxy = new V4L2CameraProxy(index, camera);
> 
> (note, I'm asking if your series makes this possible, not for you to
> make this change)

If you drop patch 2/3, yes, that's what would happen. Both you and
Niklas seem to prefer that option, so that's what I'll do in v2.

> Otherwise, I like that the index becomes part of the iteration.
> I have a slight dislike to treating your iterated item as 'value' ...
> but that's just the same dislike I have for std::pair, but at least in
> this case it's not named first and second!
> 
> Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
> 
> > +		V4L2CameraProxy *proxy = new V4L2CameraProxy(camera.index,
> > +							     camera.value);
> >  		proxies_.emplace_back(proxy);
> > -		++index;
> >  	}
> >  
> >  	return 0;
> > @@ -117,11 +118,10 @@ int V4L2CompatManager::getCameraIndex(int fd)
> >  	if (!target)
> >  		return -1;
> >  
> > -	unsigned int index = 0;
> > -	for (auto &camera : cm_->cameras()) {
> > -		if (camera == target)
> > -			return index;
> > -		++index;
> > +	auto cameras = cm_->cameras();
> > +	for (const auto camera : utils::enumerate(cameras)) {
> > +		if (camera.value == target)
> > +			return camera.index;
> >  	}
> >  
> >  	return -1;

-- 
Regards,

Laurent Pinchart