emplace-based version of Nullable

[FeepingCreature]

On Wednesday, 27 June 2018 at 12:49:20 UTC, FeepingCreature wrote:
> Maybe it's finally time to write an emplace-based version of 
> Nullable?

Having done so: is it better to have just the moveEmplace 
Nullable, or use standard opAssign for implicitly constructable 
types? This would let Nullable handle horrible things like 
structs that do things with pointers to their members. On the 
other hand, it's extra complexity.

Branch here: 
https://github.com/dlang/phobos/compare/master...FeepingCreature:Nullable-use-moveEmplace

Comments?