Re: [boost] [variant2] Andrzej's review -- documentation

Subject: Re: [boost] [variant2] Andrzej's review -- documentation
From: Peter Dimov (pdimov_at_[hidden])
Date: 2019-04-07 03:33:00

Andrzej Krzemienski wrote:
> Consider the following example:
>
> ```
> struct X {};
>
> struct Guard {
>     explicit Guard(int) {}
>     Guard(Guard&&) = delete;
> };
>
> variant<X, Guard> v {};
> v.emplace<Guard>(1);
> ```
>
> This works fine with std::variant, but fails to compile with 
> variant2::variant, because the latter requires all the alternative types, 
> at least in one implementaiton of the never-empty trick, to be 
> move-constructible. But this requirement is never listed in either global 
> requirements for alternative types stored in variant, or in the 
> specification of functions `emplace()`.

The documentation is correct, the implementation is wrong here; this should 
work and the fact that it doesn't is a bug. Thanks.