Re: [boost] [variant] Warning: variadic templates in boost::variant

Subject: Re: [boost] [variant] Warning: variadic templates in boost::variant
From: Andrey Semashev (andrey.semashev_at_[hidden])
Date: 2013-12-09 07:16:37

On Monday 09 December 2013 14:02:12 Peter Dimov wrote:
> Antony Polukhin вроте:
> > However this:
> > * breaks ABI (now variant is declared as `template <typename T0,
> > typename... TN> class variant`)
> 
> Why not just template<class... TN> class variant? It's true that the
> degenerate case of variant<> isn't particularly useful, but then again,
> neither is the singular case of variant<X>. Is there a good reason to
> prohibit variant<>?

What should be the storage for such a variant then? Also, most of the 
interface of variant<> becomes invalid (e.g. type(), which(), assignment from 
elements, apply_visitor()). With such drastic interface differences, there 
should be a compelling reason to have such a specialization, and I don't see 
one.