Nullable or Optional? Or something else?

[Steven Schveighoffer]

On Wed, 02 Sep 2009 16:54:30 -0400, Andrei Alexandrescu  
<SeeWebsiteForEmail at erdani.org> wrote:

> grauzone wrote:
>> Andrei Alexandrescu wrote:
>>> I plan to add a Nullable struct to Phobos (akin to C#'s Nullable,  
>>> Boost's Optional).
>>>
>>> Apparently a good design is to define Optional!T with a minimum of  
>>> member functions (ideally none) and have it use the "alias this"  
>>> feature to masquerade as a T. That way Optional!T looks and feels much  
>>> like a T, except that it supports a function
>>  I still don't understand how one can feel comfortable with the fact,  
>> that "alias this" can overshadow arbitrary members of the alias'ed type.
>
> That's why I want to add no member functions to Optional. The test for  
> null will be a free function.

How does Optional!valuetype support this:

Optional!valuetype x;
x = null;

Don't you need opAssign?

-Steve