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: Andrzej Krzemienski (akrzemi1_at_[hidden])
Date: 2017-06-14 16:28:18

2017-06-14 18:21 GMT+02:00 Peter Dimov via Boost <boost_at_[hidden]>:

> Andrzej Krzemienski wrote:
>
> If you are not doing double buffering, how can you guarantee that
>> `emplace` is strong? You move the original to the side?
>>
>
> I could do that, but I construct on the side instead and move it into
> place. This is another instance where people may disagree because emplace
> should as a principle always construct in-place. But realistically,
> construct on the side + move is never inferior to move original to the
> side, construct in-place, optionally move original back if constructor
> throws.
>

Given that you have to move something anyway, I guess you are right.

Now I realize this all means the types inside variant need to be movable.
This will not be a problem in most of the cases, but does it mean I cannot
use variant2 with non-movable types?

Regards,
&rzej;