Disallow null references in safe code?

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On Tuesday, 4 February 2014 at 14:54:35 UTC, Adam D. Ruppe wrote:
> On Tuesday, 4 February 2014 at 14:34:49 UTC, Idan Arye wrote:
>> Probably because `Nullable!` suggests that's it's a library 
>> solution - and it isn't.
>
> It should be. The way I'd do it is
>
> Object o; // not null
> @nullable Object o; // like we have today
>
> BUT, user code would never use that. Instead, we'd have:
>
> struct Nullable(T) if(__traits(compiles, (@nullable T) {}) {
>    @nullable T;
> }
>
> // and a corresponding one so stuff like Nullable!int works
>
>
> This gives us:
>
> * Implementation help - no binary cost for Nullable!Object 
> since it just uses null directly instead of a bool isNull field 
> (the optimizer also knows this)
>
> * Consistency with all other types. Nullable!int works, 
> Nullable!Object can be passed to a template, inspected, etc. 
> without new traits for isNullable and everything.
>
> * Library functionality so we can also make other types that do 
> the same kind of thing
>
>
> Then, if we did the Type? syntax, it would just be rewritten 
> into Nullable!Type. Nullable's definition would probably be in 
> the auto-imported object.d so it always works.

I'm interested in how this might fit in with your recent 
discovery in this thread:

http://forum.dlang.org/thread/majnjuhxdefjuqjlpbmv@forum.dlang.org?page=1