[boost] variant2 - really dumb way off topic question here

Subject: [boost] variant2 - really dumb way off topic question here
From: Robert Ramey (ramey_at_[hidden])
Date: 2019-02-22 22:47:15

On 2/22/19 9:48 AM, Peter Dimov via Boost wrote:
> I'd like to request a formal Boost review for the Variant2 library,
> https://github.com/pdimov/variant2. Variant2 contains an implementation 
> of a
> variant<T...> type that is an almost conforming std::variant, except it
> doesn't require C++17 and supports C++11 and above.
> 
> It's also never valueless and has a few other extensions.

I see optional, expected, outcome and .. (monad?) as just special cases 
of variant. for example

template<typename T>
using optional = variant<false_type, T>;

Why is it necessary to have all these type implemented?  Can't there be 
some sort of "base" type which can be used to implement all these others?

Robert Ramey