Re: [boost] variant2 never empty guarantees (was: Re: Outcome/expected/etc/etc/etc)

Subject: Re: [boost] variant2 never empty guarantees (was: Re: Outcome/expected/etc/etc/etc)
From: Peter Dimov (lists_at_[hidden])
Date: 2017-06-08 13:01:07

> Gottlob Frege wrote:
>
> > Agreed.  But I don't see much value in the never-empty guarantee if it 
> > doesn't give you the strong guarantee.
>
> I'm not sure I understand this fully; could you please explain from what 
> expressions, and under what conditions, you expect the strong guarantee?
>
>     variant<X, Y> v1, v2;
>     X x;
>
>     v1= v2; // do you expect strong guarantee here?
>     v1 = std::move(v2); // here?
>     v1 = x; // here?
>     v1 = std::move(x); // here?
>     v1.emplace<X>(); // here?

Anyone? This is a genuine inquiry. How can I give you strong guarantee if 
you don't tell me when and where you want it?