Re: [boost] Variant2 review

Subject: Re: [boost] Variant2 review
From: Gavin Lambert (boost_at_[hidden])
Date: 2019-04-08 00:56:19

On 8/04/2019 05:03, Peter Dimov wrote:
> Phil Endecott wrote:
>> - I would love to have some way to get a warning or error if the 
>> double storage mode had been triggered, or to disable that mode (with 
>> an error).
> 
> I was thinking of addressing this by adding either
> 
>  Â Â  static constexpr bool variant<T...>::is_single_buffered();
> 
> or
> 
>  Â Â  static constexpr bool variant<T...>::is_double_buffered();
> 
> (not sure which spelling is better), so that you can static_assert that 
> your variants are never double-buffered.

Something like this would definitely be nice.

Especially when something as simple as accidentally omitting "noexcept" 
can cause a significant behavioural and storage size change, it's great 
to be able to tell the compiler that this was unintended.

(Of course, as I've said before I would have preferred that this choice 
was made by providing two different front-end "variant" types -- that 
way the assert is already inside the library and the user can't forget 
to make it.)