Re: Mother of all Variants

From: David Sankel (camior_at_[hidden])
Date: 2019-06-27 19:57:23

On Thu, Jun 27, 2019 at 2:11 AM Alexander Grund via Boost <
boost_at_[hidden]> wrote:

>
> Am 27.06.19 um 04:03 schrieb David Sankel via Boost:
> > On Wed, Apr 17, 2019 at 8:42 AM Andrzej Krzemienski via Boost <
> > boost_at_[hidden]> wrote:
> >
> >> wt., 16 kwi 2019 o 23:57 Richard Hodges via Boost <
> boost_at_[hidden]>
> >> napisał(a):
> >>
> >>> Are there real-world examples of well-designed classes who's move
> >>> assignment operators throw?
> >>>
> >>> I think if I saw that in a code review I'd be inclined to demand a
> >>> different design choice.
> >>>
> >>> Is there a good reason that variants should support such classes?
> >>>
> >> Some implementations of std::list throw from their move constructors and
> >> default constructors. I understand that the implementation is easier if
> >> even an empty list has a dummy node, which requires allocation.
> >>
> > Also classes that use the PIMPL idiom.
>
>
> If a class uses PIMPL and does a move, isn't that just a pointer swap
> which cannot throw? Or would that be implemented as another allocation
> in the moved-from class? I can't imagine why.
>

Move assignment is fine. Move construction is where allocation would need
to happen so the "moved from" object stays in a valid state.