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From: Andrea Coccoli <A.M.Coccoli@ncl.ac.uk>
Subject: Using Controlled type objects.
Date: 1996/08/01
Message-ID: <32008E75.6A3F@ncl.ac.uk>#1/1
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organization: University of Newcastle upon Tyne
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newsgroups: comp.lang.ada
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Date: 1996-08-01T00:00:00+00:00
List-Id: <comp.lang.ada>


Hi everybody,
I'm implementing a recoverable object in Ada95.
For the stack, I'm using the generic one provided by the Lovelace Tutor

GENSTACK.ADS

  with Ada.Finalization; use Ada.Finalization;

  generic
    type Item is private;  
  package GenStack is
    -- This implements a simple generic stack of Items.
    -- (C) 1996 David A. Wheeler.

    type Stack is new Controlled with private;
		      #	
    type Stack_Access is access all Stack'Class;
    function ..
    ...
 
  private 
    type Stack_Node;
    type Stack_Node_Access is access Stack_Node;
    type Stack is new Controlled with record
		      #
          Start : Stack_Node_Access;
        end record;
    procedure Adjust(Object : in out Stack);
    procedure Finalize(Object : in out Stack);
  end Generic_Stack;


GENSTACK.ADB

 package body GenStack is

    type Stack_Node is record
           Data : Item;
           Next : Stack_Node_Access;
        end record;
....

What I want to do is to create an object which could give me the chances
to save and to restore its state. My first idea was to have a generic
package, in order to achieve reusability. So I defined:

REUSABLE.ADS

with genstack;
generic

type item is private;

package reusable is

        package lstack is new genstack(Item);
        --use lstack;
        type local is tagged limited private; 
	...

private
        type local is tagged limited
                record
                state : Item;
                stc : lstack.stack;
                end record;
	...

The problems arise when I want to declare an instantiation of this
package:

EXAMPLE.ADB

with reusable;
procedure example is

	package myreusable is new reusable(character);
	...

When I compile it, I receive this message:
genstack.ads:#: controlled type must be declared at the library level 

(I've marked with # the point indicated by the compiler).

The question is: how can I keep on using the same structure and the
controlled type without such an error message?
Or, is there another solution?
I hope I didn't annoy you with silly questions,

Cheers,

	Andrea