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From: dgibson@snoopy.cis.ohio-state.edu (david scott gibson)
Subject: Q. on Automatic Package Finalization
Date: 1996/09/22
Message-ID: <523tt4INNlu7@snoopy.cis.ohio-state.edu>#1/1
X-Deja-AN: 184610073
organization: The Ohio State University,
 Department of Computer and Information Science
newsgroups: comp.lang.ada
Date: 1996-09-22T00:00:00+00:00
List-Id: <comp.lang.ada>


Hi.  Does anyone know of a good way to achieve automatic package
finalization in Ada95?  I'd like to create a generic package which
automatically cleans up its package instance state (possibly including
allocated memory, temporary files, etc.) when the package scope ends.
The code below (which compiles under GNAT 3.05) is one attempt to
achieve this using controlled types.  It requires that the
representation of state for package P instances be incorporated into
an instance (pkg_var) of a controlled type (PC.T) declared
in a library-level package (PC).  This is not a very satisfactory
solution even if it would work.  Does anyone have some better
ideas for handling automatic package finalization?

Dave
--
dgibson@cis.ohio-state.edu

----------------------------------------
-- pc.ads

with Ada.Finalization;

package PC is               -- library level since controlled

    type T is new Ada.Finalization.Controlled with 
        record
            rep: Integer;   -- representation for pkg P's variables
        end record;         -- non-privtate for P direct access
                       
    procedure Finalize(     
            x: in out T
        );

end PC;

----------------------------------------
-- pc.adb

with Ada.Text_IO;

package body PC is

    procedure Finalize_Package (x: in out T) is
    begin
        Ada.Text_IO.Put_Line("Finalizing package P");
        x.rep := 0;
    end Finalize_Package;

    procedure Finalize(
                x: in out T
            ) is
    begin
        Finalize_Package(x);
    end Finalize;

end PC;

----------------------------------------
-- p.ads

with PC;

generic

package P is

    type T is private;

    procedure Initialize_Package (x: in out PC.T);

private

    type T is 
        record
            rep: PC.T;
        end record;

end P;

----------------------------------------
-- p.adb

with Ada.Text_IO;

package body P is

    pkg_var: PC.T; 

    procedure Initialize_Package (x: in out PC.T) is
    begin
        Ada.Text_IO.Put_Line("Initializing package P");
        x.rep := 1;
    end;

begin
   Initialize_Package(pkg_var);
end P;

----------------------------------------
-- ptest.adb

with P;

procedure PTest is                -- output:

    package PI1 is new P;         -- Initializing package P

begin

    declare
        package PI2 is new P;     -- Initializing package P
    begin
        null;
    end;                          -- Finalizing package P

end PTest;                        -- Finalizing package P