[vile]

It's not shorter than out-of-the-box c# 6, which would be var id = order?.Customer?.Id ?? "INVALID";

I think that was the point he was making, that it's always been possible, and now is simple.

[lacampbell]

Except that nullable types aren't the same thing as option types, so it's not doing the same thing. Nullables are much weaker than options. You can't do this for instance:

    string? id = "Name";

While you can do stuff like this:

   int x = 0;
   int? y = x;

Again, F# has nullable types and options, and the fact that no one in F# uses nullable types should tell you something.