Re: Not null feature with anonymous and named access types

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

On 14 Jun 2006 20:48:28 -0700, Anh Vo wrote:

> Dmitry A. Kazakov wrote:
>> On 14 Jun 2006 08:37:13 -0700, Anh Vo wrote:
>>
>> via *this* pointer, which does not mean that it cannot be reclaimed at all.
>> Consider trivial stack allocated aliased variable.
> 
> I am afraid I do not understand "this* pointer means.

You can have many pointers and other references to the same memory.

> What I was
> talking about not null access object using heap memory, not aliased
> variable at all. See my code snipet from my original post.

That's no problem. You just shouldn't mix referencing objects and memory
management. Not-null access types aren't intended for memory management. So
your example is flawed [*].

>> No, you just don't use not-null pointers where deallocation is possible /
>> necessary. That's the very idea of not-null pointers.
> 
> I weight memory leak more important than convenient way of using null
> excluded pointer. I am fine with not null pointer pointing to an
> aliased object. In this case, attemptingp to deallocate the pointer is
> clearly a language violation.

But an aliased object, in a wider sense, that you have a more than one
reference to it, is the only case where non-null pointer should be used!

--------------
* There is a language design problem that not-null is a subtype constraint
rather than a type, so Ada.Unchecked_Deallocation cannot reject
instantiation with a not-null pointer, as it probably should. But that is a
problem of generics, not of null-pointers. But this is another story.

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