[libcamera-devel] [PATCH 01/11] Fixes Bug 156, which breaks libcamera on Android < 12.

[Kieran Bingham]

Quoting Naushir Patuck (2022-10-26 09:46:51)
> Hi,
> 
> On Wed, 26 Oct 2022 at 09:24, Kieran Bingham via libcamera-devel <
> libcamera-devel at lists.libcamera.org> wrote:
> 
> > Quoting Nicholas Roth (2022-10-26 02:50:34)
> > > Another possible fix is to cast libcamera::utils::Duration to
> > > std::chrono::duration before performing division. I've tested that and it
> > > works. Would folks be amenable to that instead?
> >
> > That sounds like we still have to make global updates. Are any of those
> > locations where we should store a libcamera::utils::Duration instead of
> > a std::chrono::duration to prevent having to cast?
> >
> > If casting works around the issue, is it sufficient / possible to
> > provide an explicit casting operator? (I've never done this to more than
> > the POD types, but it 'looks' like you can specify specific target
> > classes as an operator?)
> >
> >   https://en.cppreference.com/w/cpp/language/cast_operator
> 
> 
> Casting like this is indeed possible, but even then, the changes required
> are spread across the codebase.  IMO this is undesirable for readability,
> and error prone as any future developers must know to do this cast
> if they were to do computations with utils::Duration.
> 
> I hope there is a centralized solution with operator / overloading, but
> if there's no choice...

ahh, I thought that would allow the compiler to do the implicit casting,
if the type was defined.

But perhaps the clue is in the name "cast_operator"

--
Kieran

> 
> Naush
> 
> 
> >
> > Something like (I have no idea if this is something that can work, or if
> > it helps the compiler as it should already know the type?!)...:
> >
> > class Duration : public std::chrono::duration<double, std::nano>
> > {
> > ...
> >
> >         explicit operator std::chrono::duration() {
> >                 return std::chrono::duration_cast<BaseDuration>>(*this);
> >         }
> >
> > or perhaps 'worse' ? (but at least isolated to here in the class?)...
> >
> >         constexpr explicit operator double() {
> >                 return get<std::nano>();
> >         }
> >
> > ...
> > }
> >
> > --
> > Kieran
> >