SumType in Phobos?

[Ernesto Castellotti]

How about including SumType (https://github.com/pbackus/sumtype) 
in Phobos?

We know that std.variant.Algebraic has problems (nogc, nothrow 
etc), SumType would be a wonderful solution to provide a tagged 
union in the std.

In my opinion it could be put without too many changes in 
std.experimental.sumtype, it already has unittest and good 
documentation.

I think it's a good starting point to start modernizing phobos to 
make it even more functional and suitable for everything.