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: 2017-06-14 13:27:43

Andrzej Krzemienski wrote:

> So, you mean -- unless I am using the special "valueless" type -- all 
> assignments/emplacements/swaps are strong (possibly at the expense of 
> double buffering in some cases)? That is, there is no  "get C upon 
> unsuccessful assignment of A to B"?

The only situation in which you get a C is when C is the special `valueless` 
type, yes. This does not mean that all assignments are strong. In

    variant<vector<string>> v1, v2;

    v1 = v2;

the assignment is basic, because that's the guarantee 
vector<string>::operator= gives.