null and type safety

[Steven Schveighoffer]

"Walter Bright" wrote
> Jarrett Billingsley wrote:
>> Don't you think that eliminating something that's
>> always a bug at compile time is a worthwhile investment?
>
> Not always. There's a commensurate increase in complexity that may not 
> make it worth while.
>
> My focus is on eliminating bugs that cannot be reliably detected even at 
> run time. This will be a big win for D.

I was working in C# today, and I realized one very excellent design 
advantage for D -- the array.  In C#, if null, an array is subject to null 
dereference errors.  In D, it simply doesn't happen, because the array has a 
guard that is stored with the reference -- the length.  I think these 
similar to the kinds of things that Jarrett is referring to.  Something 
that's like a pointer, but can't ever be null, so you never have to check it 
for null before using it.  Except Jarrett's idea eliminates it at compile 
time vs. run time.

Couldn't one design a struct wrapper that implements this behavior? 
Something like:

NonNullable!(T)
{
   opAssign(T t) {/* make sure t is not null */}
   opAssign(NonNullable!(T) t) {/* no null check */}
   ...
}

-Steve