[libcamera-devel] Usage of C++17 in the public API (was "[PATCH] cam: convert to libfmt")

[Eric Curtin]

On Sat, 28 May 2022 at 00:19, Christian Rauch via libcamera-devel
<libcamera-devel at lists.libcamera.org> wrote:
>
>
>
> Am 22.05.22 um 11:52 schrieb Laurent Pinchart via libcamera-devel:
> > On Sun, May 22, 2022 at 11:08:27AM +0100, Kieran Bingham wrote:
> >> Quoting Laurent Pinchart (2022-05-10 14:04:57)
> >>> On Tue, May 10, 2022 at 01:59:37PM +0100, Eric Curtin via libcamera-devel wrote:
> >>>> On Tue, 10 May 2022 at 11:10, Kieran Bingham via libcamera-devel wrote:
> >>>>> Quoting Naushir Patuck (2022-05-10 10:49:14)
> >>>>>> On Tue, 10 May 2022 at 08:16, Tomi Valkeinen via libcamera-devel wrote:
> >
> > [snip]
> >
> >>>>>> For what it's worth, I absolutely loathe formatting in std iostream, and
> >>>>>> libfmt is a wonderful alternative.
> >>>>>> It also is close enough to the C++20 std::format implementation that
> >>>>>> eventual porting would be low effort.  So I am all for this change :)
> >>>
> >>> It's going to take a while before we can switch to C++20, but I'm
> >>> looking forward to it (and before that to some of the C++17 features
> >>> too, it would be nice to use std::optional in the public API).
> >>
> >>
> >> So, I've just seen as Christian said - we already do!
> >>
> >> It's used by color space ..
> >
> > Oops...
> >
> >> So we're faced with either reverting, or rolling back on the color-space
> >> change, or pushing forwards with C++17 on the public-api.
> >
> > Switching to C++17 worries me as it's fairly recent and may not be
> > easily available for all users. std::optional could easily rbe replaced
> > with a custom implementation in utils::optional if needed. I'm tempted
> > to leave std::optional in for now, and accept new users of std::optional
> > but no other C++17 APIs. Switching to utils::optional for ColorSpace
> > would cover new users of std::optional so we're not creating any new
> > liability.
>
> I think that C++17 is quite old by now (nearly 5 years) and all major
> compilers support it for multiple versions and years now. Do you know of
> an example, where requiring C++17 would hinder the adaptation of
> libcamera? Do any of the target system not support this standard?
>
> I think the use of std::optional to express invalid values is quite
> significant compared to the previous solution of using default
> constructed values. Reimplementing this in libcamera would be a
> solution, but it just adds development and maintenance costs for no
> obvious reason (to me).
>
> >
> >> Maybe this deserves it's own thread...
> >
> > Done :-)
> >
> >>>> I am all in for this change also, personally I would have changed to
> >>>> printf for now
> >>>> to have one less dependency (also an easy port to C++20 std::format). The
> >>>> dependency list is getting large, I noticed a build of mine failing
> >>>> recently because
> >>>> I didn't have libyaml.
> >>>
> >>> I've posted a patch that falls back to a subproject in that case. Would
> >>> you be able to give it a try ?
> >>>
> >>>> But std::format and libfmt are quite fast and anything is better than
> >>>> streams so +1.
> >>>>
> >>>>> I've never used (yet) {fmt}, but I've only heard good things about
> >>>>> performance, and of course it's headed into the standard, so I also
> >>>>> think there is some good merit to be found in this development.
> >
>

Only speaking for the red hat distros, every distro that has a package
built for libcamera or could have in future has at least C++17,
including newly released LTS release RHEL9.

Given libcamera is still 0.0 it could be a nice opportunity to take.