null [re: spec#]

[Denis Koroskin]

On Mon, 08 Nov 2010 12:08:01 +0300, Simen kjaeraas  
<simen.kjaras at gmail.com> wrote:

> Eric Poggel <dnewsgroup2 at yage3d.net> wrote:
>
>> On 11/6/2010 6:50 AM, bearophile wrote:
>>> foobar:
>>>
>>>> Any type can be wrapped by an OPTION type. trying to do the converse  
>>>> of this is impractical and is bad design.
>>>
>>> Discussing this is a waste of time now, this part of the D language  
>>> will probably never change.
>>> This is why other people and me are proposition something different.
>>>
>>> Bye,
>>> bearophile
>>
>> I still live in D1 land, so forgive me if I'm out of the loop--but what  
>> keeps this from being implemented at the library level as templated  
>> type:  NotNull!(T) ?  If there are limitations, maybe these areas of  
>> the language can be improved to get us there?
>
> NotNull!T needs to have its default constructor disabled. That is the #1
> blocker. There are other problems, mostly related to this - classes and
> structs with NotNull!T fields must define a constructor, and for structs
> that means the default destructor either needs to be possible to define
> or possible to disable. Arrays of NotNull!T may not be resized to a
> greater length, as that would require calling the default constructor of
> NotNull!T.
>
> I think that's it.
>

Not exactly disabled. The following should work:

class Foo
{
     this() {
         bar = new Object();
     }

     NonNull!(Object) bar; // fine here
}

while the following shouldn't:

NonNull!(Object) bar; // error here
bar = new Object();