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From: Dmitry A. Kazakov <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Type conversions on pool-specific access types
Date: Mon, 13 Oct 2003 12:34:41 +0200
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Date: 2003-10-13T12:34:41+02:00
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Hi all!

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 statically known?

It is a real pain to use Unchecked_Conversion for:

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.

----------------
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:

type Base_Specific_Ptr is access Base;
for Base_Specific_Ptr'Storage_Pool use ...;
...
procedure Finalize (Object : in out Base) is
begin
   -- How to get a Base_Specific_Ptr to Object?
   -- We know that it is in the pool, but the compiler does not!

This requires general to pool-specific conversion. Which could
probably be non-portable, if Unchecked_Conversion is used to
Object'Unchecked_Access to Base_Specific_Ptr. (?)

---
Regards,
Dmitry Kazakov
www.dmitry-kazakov.de