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From: Yves Bailly <kafka.fr@laposte.net>
Subject: "User-Defined Assignment" question
Newsgroups: comp.lang.ada
Date: Sat, 12 Aug 2006 10:05:57 +0200
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Date: 2006-08-12T10:06:22+02:00
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Hello all,

Here's a behaviour that sounds strange to me. After carefully reading
the ARM (7.6), I'm not sure if it's legal or not.

Here's a package spec:
--8<-----8<-----8<-----8<-----8<-----8<-----8<-----8<---
with Ada.Finalization; use Ada.Finalization;
with System.Storage_Elements; use System.Storage_Elements;
package Pkg is
   type T is new Controlled with
   record
      self: Integer_Address;
      id  : Natural;
   end record;
   overriding
   procedure Initialize(tt: in out T);
   overriding
   procedure Adjust(tt: in out T);
   overriding
   procedure Finalize(tt: in out T);
end Pkg;
--8<-----8<-----8<-----8<-----8<-----8<-----8<-----8<---

Here's the body:
--8<-----8<-----8<-----8<-----8<-----8<-----8<-----8<---
with Ada.Text_IO; use Ada.Text_IO;
package body Pkg is

   overriding
   procedure Initialize(tt: in out T) is
   begin
      tt.self := To_Integer(tt.id'Address);
      Put_Line("Initialize " &
         Integer_Address'Image(tt.self));
   end Initialize;
    
   overriding
   procedure Adjust(tt: in out T) is
   begin
      tt.self := To_Integer(tt.id'Address);
      Put_Line("Adjust " &
         Integer_Address'Image(tt.self));
   end Adjust;
   
   overriding
   procedure Finalize(tt: in out T) is
   begin
      tt.self := To_Integer(tt.id'Address);
      Put_Line("Finalize " &
         Integer_Address'Image(tt.self));
   end Finalize;

end Pkg;
--8<-----8<-----8<-----8<-----8<-----8<-----8<-----8<---

So basically, each procedure prints a message showing which instance of
Pkg.T it is given.

Now a small test program:
--8<-----8<-----8<-----8<-----8<-----8<-----8<-----8<---
with Ada.Text_IO; use Ada.Text_IO;
with Pkg;
procedure Test is
   function Func return Pkg.T is
      dummy: Pkg.T;
   begin
      Put_Line("    Func");
      return dummy;
   end Func;
   tt_1: Pkg.T;
begin
   Put_Line("----- START");
   tt_1 := Func;
   Put_Line("----- END");
end Test;
--8<-----8<-----8<-----8<-----8<-----8<-----8<-----8<---

And finally the output:
--8<-----8<-----8<-----8<-----8<-----8<-----8<-----8<---
Initialize  3218775648
----- START
Initialize  3218775520
    Func
Adjust  134660136
Finalize  3218775520
Finalize  3218775648
Adjust  3218775648
Finalize  134660136
----- END
Finalize  3218775648
--8<-----8<-----8<-----8<-----8<-----8<-----8<-----8<---

What seems strange to me is that there is an "Adjust" and a "Finalize"
call on an object which has never been "Initialize"d... look at the
instance identified by 134660136. I guess is some temporary anonymous
object. If I understand well ARM 7.6, the clause 7.6-23/2 seems to tell
that omitting the Initialize call is *not* permitted...

What do you think?

This has been tested using GNAT 2006.

Best regards,

-- 
(o< | Yves Bailly  : http://kafka-fr.net   | -o)
//\ | Linux Dijon  : http://www.coagul.org | //\
\_/ |                                      | \_/`