SumType in Phobos?

[Per Nordlöw]

On Thursday, 20 February 2020 at 17:14:13 UTC, Paul Backus wrote:
> The amount of @trusted code is also a red flag. I've already 
> found one mistake in it [1], which means there are probably at 
> least a couple more that I didn't catch.
>
> [1] 
> https://github.com/nordlow/phobos-next/blob/master/src/nxt/variant.d#L226-L228

I see now that the private function `as` should be qualified as 
@system.

Is this the mistake you are thinking about?