From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Unchecked_Deallocation with tagged class type.
Date: Wed, 15 Nov 2023 22:17:37 +0100 [thread overview]
Message-ID: <uj3chf$1tbp8$1@dont-email.me> (raw)
In-Reply-To: <uj39gv$1srlq$1@dont-email.me>
On 2023-11-15 21:26, Blady wrote:
> Le 14/11/2023 à 23:42, Dmitry A. Kazakov a écrit :
>>> But what does "Finalize (OB);"?
>>
>> Crashes your program. It is a bug. You should instantiate
>> Unchecked_Deallocation with class-wide type if you pass a class-wide
>> pointer.
>
> Thanks, I haven't considered this possibility.
> Note: the previous program built with GNAT FSF 13.2.0 ran without
> exception.
>
> I've changed:
> with Ada.Unchecked_Deallocation;
> procedure test_20231113_free_class is
>
> type TTA is tagged record
> AA : Integer;
> end record;
> type ATTA is access all TTA;
> type CATTA is access all TTA'Class;
> procedure Finalize (O : in out CATTA) is
> procedure Free is new Ada.Unchecked_Deallocation (TTA'Class, CATTA);
> begin
> Free (O);
> end Finalize;
>
> type TTB is new TTA with record
> BB : Integer;
> end record;
> type ATTB is access all TTB;
> type CATTB is access all TTB'Class;
> procedure Finalize (O : in out CATTB) is
> begin
> Finalize (CATTA (O));
> end Finalize;
>
> OA : CATTA := new TTA;
> OB : CATTB := new TTB;
>
> begin
> Finalize (OA);
> Finalize (OB);
> end test_20231113_free_class;
>
> It runs without exception.
> One question remains about "Finalize (OB);":
> Which memory size is deallocated TTA'Size or TTB'Size?
It is a wrong question. The implementation of the pool may ignore size
using the block size instead. Furthermore T'Size is not necessarily the
size actually allocated.
Regarding Unchecked_Deallocation instantiated with a pointer to a
class-wide object, consider it dispatching on the target object tag.
Thus you can deallocate any object using any instance of
Unchecked_Deallocation for any class-wide parent of, interfaces included.
So Finalize (OB) is OK.
--
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de
next prev parent reply other threads:[~2023-11-15 21:17 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-11-14 21:11 Unchecked_Deallocation with tagged class type Blady
2023-11-14 22:42 ` Dmitry A. Kazakov
2023-11-15 20:26 ` Blady
2023-11-15 21:17 ` Dmitry A. Kazakov [this message]
2023-11-16 20:29 ` Blady
2023-11-17 13:12 ` AdaMagica
2023-11-17 13:13 ` AdaMagica
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