Re: Mother of all Variants

From: Alexander Grund (alexander.grund_at_[hidden])
Date: 2019-06-27 07:21:04

Am 27.06.19 um 09:06 schrieb degski via Boost:
> On Thu, 27 Jun 2019 at 09:54, Alexander Grund via Boost <
> boost_at_[hidden]> wrote:
>
>> Am 27.06.19 um 08:45 schrieb degski via Boost:
>>> As from C++11 std::swap is marked noexcept, so yes. As from C++20 it's
>> also
>>> constexpr, so now it can definitely cannot throw.
>>>
>>> degski
>> Are you sure? According to
>> https://en.cppreference.com/w/cpp/algorithm/swap this is only
>> non-throwing if it can be moved without throwing
>>
>   Yes, but std::swap must also not invalidate any references, pointers, or
> iterators referring to the elements of the containers being swapped, which
> leaves the scope for throwing rather small [if at all possible].
>
> degski

Combining it with "Some implementations of std::list throw from their 
move constructors" (David Sankel) leads to `std::swap(list1, list2)` can 
throw and hence is not `noexcept(true)`

This applies to any "strange" class whose move may throw which was the 
motivation of that (part of the) discussion.

So answering

 > Is there a good reason that variants should support such classes?

Maybe. At least it is also supported by std::move