Beginner: Unchecked Deallocation

Beginner: Unchecked Deallocation

[Antoine Lec.]

Hi all

I'm quite new to ADA, ( a few weeks) and I'm trying to write some code for 
a monodirectional linked list.

I've done several function which satisfies me, althought I think
my style is not in the Ada phylosophy.

The first true problem i've encountered is this one: I want to destroy
my linked list, so i would like to free each link in the list.
I think that I have to use Ada.Unchecked.Deallocation()
My procedure:

   procedure Free is
   new Ada.Unchecked_Deallocation (Liste, Liste_Acs);

works fine when I put this code directly in the main program, but that's not
my goal; I didn't manage to put this procedure, like the other functions, 
in the body and in the specification parts of my package.
When I try to do that, i got this error:

 package body LCM is
                |
   >>> missing body for "Free" declared at lcm.ads:28

I don't understand (maybe because of misunderstanding of the Generic concept ?)

Is this procedure supposed to have a "body" ? I thought the body was provided by
the instanciation of the generic procedure ? (I'm not sure about the exact terms)

Thanks for any help or commments on my code !
(I think my code is clear enough not to translate the name of my functions into
english)

Here come my code:

/***************************************************************
*                     FICHIER LCM.ADS                          *
\***************************************************************

package LCM is
   type Liste;
   type Liste_Acs is access Liste;
   type Liste is
      record
         Item : Integer;
         Suiv : Liste_Acs;
      end record;
   Liste_Vide: exception;

   function
     Insere_Tete
     (Ls   : in     Liste_Acs; Item : in     Integer    )
     return Liste_Acs;

   function
     Insere_Ordre
     (Ls   : in     Liste_Acs; Item :        Integer    )
     return Liste_Acs;

   procedure
     Affiche (Ls : in     Liste_Acs );

   function
     Supprime_Tete (Ls: in  Liste_Acs)
                   return Liste_Acs;

   procedure Free;

end LCM;


/***************************************************************
*                        FILE LCM.ADB                          *
\***************************************************************

with Ada.Text_IO;
with Ada.Unchecked_Deallocation;

package body LCM is
   function Insere_Tete (
                         Ls   : in     Liste_Acs;
                         Item : in     Integer    )
                        return Liste_Acs is
   begin
      return new Liste'(Item, Ls);
   end Insere_Tete;

   function Insere_Ordre (
                          Ls   : in     Liste_Acs;
                          Item :        Integer    )
                         return Liste_Acs is
   begin
      if Ls=null
      then
         return Insere_Tete(Ls,Item);
      elsif Item <= Ls.Item then
         return Insere_Tete(Ls,Item);
      else
         return new Liste'(Ls.Item, Insere_Ordre(Ls.Suiv,Item));
      end if;
   end Insere_Ordre;

   function Supprime_Tete (Ls: in  Liste_Acs)
                          return Liste_Acs
   is
   begin
      if Ls=null then raise Liste_Vide;
      else return Ls.Suiv;
      end if;

-- I would like to use the free() procedure Here, of course 

   end Supprime_Tete;


   procedure Affiche (
                      Ls : in     Liste_Acs ) is
      procedure Affiche2 (
                          Ls : in     Liste_Acs ) is
      begin
         if Ls/=null
         then
            begin
               Ada.Text_IO.Put(Integer'Image(Ls.Item));
               Affiche2(Ls.Suiv);
            end;
         end if;
      end Affiche2;
   begin
      Ada.Text_IO.Put('(');
      Affiche2(Ls);
      Ada.Text_IO.Put(" )");
      Ada.Text_IO.New_Line;
   end Affiche;

   procedure Free is
      new Ada.Unchecked_Deallocation (Liste, Liste_Acs);

--gnatmake complains that  there is no body here
   
end LCM;


-- 
b@v

Re: Beginner: Unchecked Deallocation

[Mark Doherty]

bilbo@volcanomail.com (Antoine Lec.) wrote in message news:<d442bc8e.0112171935.30eb28b1@posting.google.com>...
> My procedure:
> 
>    procedure Free is
>    new Ada.Unchecked_Deallocation (Liste, Liste_Acs);
> 
> works fine when I put this code directly in the main program, but that's not
> my goal; I didn't manage to put this procedure, like the other functions, 
> in the body and in the specification parts of my package.
> When I try to do that, i got this error:
> 
>  package body LCM is
>                 |
>    >>> missing body for "Free" declared at lcm.ads:28
> 
> I don't understand (maybe because of misunderstanding of the Generic concept ?)
> 
> Is this procedure supposed to have a "body" ? I thought the body was provided by
> the instanciation of the generic procedure ? (I'm not sure about the exact terms)
> 


Procedure free declared in the spec is parameterless. The procedure
free instantiated in the body takes an in out parameter of type
liste_acs!

Re: Beginner: Unchecked Deallocation

[Antoine Lec.]

> Procedure free declared in the spec is parameterless. The procedure
> free instantiated in the body takes an in out parameter of type
> liste_acs!


There is another problem when I change the definitions with this one :

lcm.ads:
procedure Free (LS: in out Liste_Acs);

lcm.adb
procedure Free (LS: in out Liste_Acs) is
new Ada.Unchecked_Deallocation (Liste, Liste_Acs);

This results with:

  procedure Free (LS: in out Liste_Acs) is
                 |
>>> formal part not allowed in instantiation

So what's the problem ?

-- 
b@v

Re: Beginner: Unchecked Deallocation

[Patrick Hohmeyer]

Antoine Lec. wrote :

> > Procedure free declared in the spec is parameterless. The procedure
> > free instantiated in the body takes an in out parameter of type
> > liste_acs!
> 
> 
> There is another problem when I change the definitions with this one :
> 
> lcm.ads:
> procedure Free (LS: in out Liste_Acs);
> 
> lcm.adb
> procedure Free (LS: in out Liste_Acs) is
> new Ada.Unchecked_Deallocation (Liste, Liste_Acs);
> 
> This results with:
> 
>   procedure Free (LS: in out Liste_Acs) is
>                  |
> >>> formal part not allowed in instantiation
> 
> So what's the problem ?
> 

You have to write 
lcm.ads:
procedure Free (LS: in out Liste_Acs);

and

lcm.adb
procedure Free is new Ada.Unchecked_Deallocation (Liste, Liste_Acs);

But WHY the heck do you put Free in the ads anyway?
Do you really want the main procedure to dangle with the lists pointers?

Thumb rule : nothing that directly manipulates pointers in an ads.
Just hide it in the adb. (Unless you have a very good reason why not)

-- 
Patrick Hohmeyer

Re: Beginner: Unchecked Deallocation

[Steve Doiel]

If you move:

  procedure Free( LS: in out List_Acs ) is
    new Ada.Unchecked_Deallocation( Liste, List_Acs );

To the package spec all is well.

SteveD

"Antoine Lec." <bilbo@volcanomail.com> wrote in message
news:d442bc8e.0112181417.32159165@posting.google.com...
> > Procedure free declared in the spec is parameterless. The procedure
> > free instantiated in the body takes an in out parameter of type
> > liste_acs!
>
>
> There is another problem when I change the definitions with this one :
>
> lcm.ads:
> procedure Free (LS: in out Liste_Acs);
>
> lcm.adb
> procedure Free (LS: in out Liste_Acs) is
> new Ada.Unchecked_Deallocation (Liste, Liste_Acs);
>
> This results with:
>
>   procedure Free (LS: in out Liste_Acs) is
>                  |
> >>> formal part not allowed in instantiation
>
> So what's the problem ?
>
> --
> b@v

Re: Beginner: Unchecked Deallocation

[Antoine Lec.]

> But WHY the heck do you put Free in the ads anyway?
> Do you really want the main procedure to dangle with the lists pointers?
> 
> Thumb rule : nothing that directly manipulates pointers in an ads.
> Just hide it in the adb. (Unless you have a very good reason why not)


thanks for the advice
In fact my free() procedure had to be a local procedure in the
liste_acs freeing procedure.
So it has nothing to do in the .ads

-- 
b@v