Re: not null

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Wed, 4 Mar 2009 08:09:56 -0800 (PST), Adam Beneschan wrote:

> On Mar 4, 6:56 am, Hyman Rosen <hyro...@mail.com> wrote:
>> Georg Bauhaus wrote:
>>> As said to have been seen on /.
>>> another financial disaster, again caused
>>> by making references to nothing, in Algol W,
>>>http://qconlondon.com/london-2009/presentation/Null+References:+The+B...
>>
>> You are misreading the abstract. First of all, it's not
>> about some particular incident. He's talking about the
>> overall impact. Second, he's not talking about failure
>> to check for null references, he's talking about having
>> null references at all, so Ada is no better.
> 
> I'm having difficulty understanding the point.  You have to have the
> idea of the lack of a reference.  How else would you implement a
> linked list abstraction?

Recursive types is not the single case where references are used. For smart
pointers not null constraint is very useful. Though it is quite painful to
make use of it, because of broken initialization issues. It is also useful
for access discriminants etc. Granted, the latter shouldn't be access. I
mean it should better be:

   type T (X : Limited_Foo) is ...

rather than awful

   type T (X : not null access Limited_Foo) is ...

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de