Re: Question about OO programming in Ada

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

On Thu, 04 Dec 2003 16:32:17 -0500, "Robert I. Eachus"
<rieachus@comcast.net> wrote:

>Dmitry A. Kazakov wrote:
>> On Wed, 03 Dec 2003 20:23:53 -0500, "Robert I. Eachus"
>> <rieachus@comcast.net> wrote:

> >                                                     This would
> > not be necessary if finalization of the type Pointer called
> > deallocator in addition to a call to Finalize.
>
>Think about this for a second, because there is a germ of a good idea 
>here.  For access types for which assignment is valid, such a rule would 
>be a disaster.  For example you don't want the next record in a linked 
>list, and for that matter all of the rest of the list, deallocated if 
>you remove an item from a list.

This actually is an argument against controlled-ness. I see little
sense in taking any actions upon access type finalization. This rule
imposes a non-zero run-time burden with practically zero gain.

>However, in my example above, the 
>Object_Ref type is declared as limited.  What if we had true limited 
>access types?
>
>type Pointer is limited access Object;
>
>For such a type deallocating the designated memory when the Pointer 
>object goes away would make sense.  I just don't think it is a necessary 
>language extension since it is so easy to create the abstraction when 
>needed.  (And besides, there are many cases where you want the type to 
>appear limited to users, but where you actually want to do assignment in 
>the package body.)

I think that a real solution is to provide proper construction /
destruction for *all* types. Should we have it, then the problem could
be reduced to developing constructors / destructor of a given access
type. This would allow a user to create any sort of garbage collection
scheme he wants, instead of forcing compiler vendors to implement more
and more sophisticated constructions.

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