RFC: std.sumtype (adding sumtype to Phobos)

[SHOO]

On Sunday, 22 November 2020 at 13:25:37 UTC, Paul Backus wrote:
> Following the recent 1.0.0 release [1], I have decided to 
> submit sumtype [2] for inclusion in Phobos, D's standard 
> library. The PR can be found here:
>
> https://github.com/dlang/phobos/pull/7702

I think SumType is better to be included in std.typecons. Rather 
than a new module, I think it is more appropriate to treat it in 
the same breath as Tuple, Unique, etc.