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From: Blady <p.p11@orange.fr>
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Subject: Unchecked_Deallocation with tagged class type.
Date: Tue, 14 Nov 2023 22:11:18 +0100
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Hello,

The following code present a Finalize procedure with a parameter of 
access tagged class type in order to deallocate the memory of the given 
parameter from the root tagged type TTA and his children.
The same for TTB which is inherited from TTA. But this Finalize call 
Finalize of TTA.
It may be not the best idea.
But let's see:

with Ada.Unchecked_Deallocation;
procedure test_20231113_free_tag 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, ATTA);
    begin
       Free (ATTA (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_tag;

The procedure Free is the instanciation of Unchecked_Deallocation with 
the tagged type TTA.
Thus the call "Finalize (OA);" deallocate the memory of object OA of 
type access class TTA.

But what does "Finalize (OB);"?
What is the memory deallocate of object OB of type TTB?

Thanks, Pascal.