Re: Free'ing dynamic abstract tagged types..

["Randy Brukardt" <randy@rrsoftware.com>]

"ldb" <ldb_nospam@hotmail.com> wrote in message
news:1158872883.994303.80430@b28g2000cwb.googlegroups.com...
> Ok, so I have this abstract tagged type called Person (for the sake of
> discussion), and I have an Access_Person (which is access all
> people'class).
>
> I have some derived types, like Man and Child, with their own added
> fields. And I have defined Access_Man, Access_Child, as normal accesses
> to these types.
>
> I want to free an Access_Person that was dynamically allocated.
> ap : Access_Person;
> begin
> ap := Access_Person(new Man);
> free(ap);
> ...
>
> I can't figure out how to write the free routine, since unchecked
> deallocation wants a pointer (presumably access_man), but all I have is
> a class-wide pointer, and I can't figure out how, or if, I can convert
> it. Does that make sense?

No. ;-)

You just free the access and let the compiler take care of it. That is, just
instantiate Unchecked_Deallocation appropriately:

    procedure Person_Free is new Ada.Unchecked_Deallocation (Person'Class,
Access_Person);

and then call it.

> Using free(ap.all), I can make an abstract function that will dispatch
> and free any nested allocations, but I can't seem to get it to free the
> record, itself.

Right, you have to do that on the pointer. You could write something like:

          procedure Free (P :  Access_Person) is
          begin
                 Free (P.all); -- Free the contents
                 Person_Free (P); -- Free the object itself.
          end Free;

but if the derived types need internal clean-up, it's better to make the
whole tree controlled and let the compiler do all of the internal clean-up:
that makes it much harder to forget.

Since you can't add Controlled to an inheritance tree after the fact, I
think that *all* tagged type trees should be derived from Controlled or
Limited_Controlled. (Otherwise, you're saying that the extensions don't need
any clean-up, which is likely to be constraining.)

                                  Randy.