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

2017-06-08 15:01 GMT+02:00 Peter Dimov via Boost :

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 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?

Maybe nobody needs the strong guarantee? This is definitely the case for my programs. I put variants in different containers. But if exception is thrown while modifying them I am destroying the entire data structure. I do not need the previous state. If I cannot put the new one, I cannot proceed anyway. (I am not saying such guarantee is useless. I just observe that the need occurred in my programs.) Regards, &rzej;