Re: [boost] [variant] Please vote for behavior

Subject: Re: [boost] [variant] Please vote for behavior
From: Krzysztof Czainski (1czajnik_at_[hidden])
Date: 2013-01-25 15:16:38

2013/1/25 Gottlob Frege <gottlobfrege_at_[hidden]>

> On Fri, Jan 25, 2013 at 10:21 AM, Dave Abrahams <dave_at_[hidden]> wrote:
>
> > >>
> > > Isn't leaving the class with it's invariants broken simply a defect?
> >
> > Yes.  IIUC the question here is whether the invariant of variant [;-)]
> > shall be weakened to accommodate efficient move semantics, thereby
> > breaking some code, or not, at some cost (the specific costs to be
> > incurred by various strategies presently under discussion).
> >
> > But I have to admit, I haven't been reading the thread all that
> > carefully, so I could be mis-understanding completely.
> >
> >
> >
>
> Instead of weakened, which is one option discussed, I would also
> characterize much of the discussion as "let's ignore that the invariant is
> broken, because no one should rely on invariants after move".
>
> If you had opinions on that aspect, you might want to weigh in. It would be
> appreciated.
>
> Tony

I think variant after move is like int without initialization:
int i;
cout << i; // don't do this
If the fact, that moved-from objects are only good for destruction or
assignment-to is accepted, then invariants for moved-from objects are
allowed to be violated.

Kris