Is the other-kind-of-null really necessary in Nullable and Variant?

[bearophile]

Idan Arye:

> When you use `std.typecons.Nullable` with a type that already 
> accept `null` values, you get two types of nulls - the 
> `Nullable`'s null state the the regular type's `null`:
>
>     Nullable!string a;
>     writeln(a.isNull()); //prints "true"
>     a = null;
>     writeln(a.isNull()); //prints "false"

Originally D dynamic arrays were almost conflated with regular 
pointers (they were seen as fat pointers). This was recently 
partially fixed (so assigning a pointer to a dynamic array is now 
forbidden), but accepting "null" for their empty literal is one 
left part of that original suboptimal design.

Time ago I have proposed to forbid "null" as literal for an empty 
dynamic array literal, an empty associative literal, or an empty 
string, and to accept only []  ""  [:] (D already has the first 
two literals and the third looks natural).

See also:
http://d.puremagic.com/issues/show_bug.cgi?id=3889
http://d.puremagic.com/issues/show_bug.cgi?id=5788
http://d.puremagic.com/issues/show_bug.cgi?id=7227

Bye,
bearophile