Keyword to avoid not null references

[Simen Kjaeraas]

On Mon, 23 Apr 2012 10:38:27 +0200, Dmitry Olshansky  
<dmitry.olsh at gmail.com> wrote:

> On 23.04.2012 12:06, Simen Kjaeraas wrote:
>> On Mon, 23 Apr 2012 09:14:12 +0200, Namespace <rswhite4 at googlemail.com>
>> wrote:
>>
>>> I made several tests with NotNull yesterday and actually they all  
>>> passed.
>>> In special cases i didn't get a compiler error but then a runtime
>>> error is better then nothing. :)
>>>
>>> But there is still my problem with this:
>>>
>>> void foo(NotNull!(Foo) n) {
>>>
>>> }
>>>
>>> void bar(Foo n) {
>>>
>>> }
>>>
>>> in my optinion it must exist a way that both
>>> NotNull!(Foo) nf = new Foo();
>>>
>>> foo(nf);
>>> bar(nf);
>>>
>>> and furhtermore
>>> Foo f = new Foo();
>>>
>>> foo(f);
>>> bar(f);
>>>
>>> compiles.
>>> We need some hack, implicit cast or compiler cast that cast or passes
>>> Foo to NotNull!(Foo).
>>>
>>> Any suggestions?
>>
>> No. The whole point of NotNull is that it should enforce not being null.
>> Allowing implicit casting from PossiblyNull to NotNull would break this.
>
> Just include obligatory run-time check when crossing null-NotNull  
> boundaries.
>

Which carries with it hidden runtime costs that are unacceptable to some.
The point of NotNull is twofold - safety (you know it's not null) and speed
(you don't need to check if it's null). The latter goes out the window if
implicit casting were allowed.