Re: Type conversions on pool-specific access types

["Nick Roberts" <nick.roberts@acm.org>]

"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message
news:7kukov45dif9p7u2ohu6ml29mu9cgu621o@4ax.com...

> Who knows any reason why conversions between pool-
> specific access types are not allowed, provided that
> the storage pools are same? Isn't storage pool static-
> ally known?
>
> It is a real pain to use Unchecked_Conversion ...

I think it's also dangerous and unnecessary.

> type Base is new Ada.Limited_Controlled with ..;
> type Base_Ptr is access Base'Class;
> for Base_Ptr'Storage_Pool use ...;
>
> procedure Foo (Object : Base_Ptr);
> ...
> type Derived is new Base with ..;
> type Derived_Ptr is access Derived'Class;
> for Derived_Ptr'Storage_Pool use Base_Ptr'Storage_Pool;
> ...
> declare
>    Ptr : Derived_Ptr := new Derived;
> begin
>    Foo (Base_Ptr (Ptr)); -- ILLEGAL!
>
> I do not understand why.

In this situation, I suggest that you do not need to declare Derived_Ptr,
since Base_Ptr can -- and generally should -- be used to point to objects of
type Derived (as well as Base).

   declare
      Ptr : Base_Ptr := new Derived;
   begin
      Foo(Ptr);

> Another thing is initialization / finalization of controlled
> objects allocated on some specific storage pool. It could
> be a great problem if a pool-specific pointer is required ...

The answer is "Don't do that!"

Finalize should finalise whatever is inside the given Object, and not deal
in any way with where (in which pool) the object resides. After the
implementation has called Finalize for the object, it will then -- when
appropriate -- call Deallocate for the object's pool, in order to deallocate
the object's storage space from the pool. Do not mess with this mechanism.

--
Nick Roberts