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From: "Magnus Sparf" <magnus-s@dsv.su.se>
Newsgroups: comp.lang.ada
Subject: Direct_IO problem -- generic package problem
Date: Thu, 12 Jul 2001 10:42:10 +0200
Organization: National Defence Research Establishment, Sweden
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Xref: archiver1.google.com comp.lang.ada:9857
Date: 2001-07-12T10:42:10+02:00
List-Id: <comp.lang.ada>

I�m new to ADA (hopefully picking up track fast) and this summer I have the
task of converting an old Ada83 application (VAX environment) to Ada95 (PC
environment).
In the very heart of this application there is a homemade database that
compiles without problem in the VAX environment. When I compile it on GNAT
3.13p in the PC environment. I get the following error:

 db.adb:58:49: actual for "Element_Type" must be a definite subtype :::(the
last line in the extract)

Extract of code (DB is a generic package and used to create a lot of
different databases):
----------------------------------------------------------------------------
-----------
package body DB is

      type FILLED_TABLES is array (SMALL_NAT range <>) of BOOLEAN;
   pragma pack (FILLED_TABLES);

      type LINE_COL is
         record
            X_V : SMALL_NAT := 1;
            Y_V : SMALL_NAT := 1;
         end record;

      type TABLE_VALUES  is array (SMALL_NAT range <>) of LINE_COL;

      type M_T             is array (SMALL_NAT range <>,
      SMALL_NAT range <>) of ITEM;
      type B_T             is array (SMALL_NAT range <>,
      SMALL_NAT range <>) of BOOLEAN;


      type MATRIX (MAX : SMALL_NAT;
      FIRST_RECORD : BOOLEAN;
      ROWS_FIRST     : SMALL_NAT;
      ROWS_LAST      : SMALL_NAT;
      COLUMNS_FIRST  : SMALL_NAT;
      COLUMNS_LAST   : SMALL_NAT) is

         record
            case FIRST_RECORD is
               when TRUE =>
               -- description of entire file with tables
                  FILLED              : FILLED_TABLES(2..MAX) :=
                  (others => FALSE);
                  DISCRIMANT_VALUES : TABLE_VALUES(2..MAX) :=
                  (others => (1, 1));
               when FALSE =>
               -- tables
                  VALUE        : M_T (ROWS_FIRST..ROWS_LAST,
                  COLUMNS_FIRST..COLUMNS_LAST);
                  ITEM_PUT  : B_T (ROWS_FIRST..ROWS_LAST,
                  COLUMNS_FIRST..COLUMNS_LAST);
                  RAD_INDEX    : R_T (ROWS_FIRST..ROWS_LAST);
                  COLUMN_INDEX : C_T (COLUMNS_FIRST..COLUMNS_LAST);
            end case;
         end record;

      package MY_DIRECT_IO is new Ada.DIRECT_IO(MATRIX);
----------------------------------------------------------------------------
-------------

If I give type MATRIX default values it compiles with warnings about Storage
constraints errors in runtime (that also occurs...). MATRIX is used at a lot
of other places further down.

Are there any quick (not dirty) solutions to this problem? My own ideas is
to create separate databases for all eight databases that uses DB (CAR_DB,
BOAT_DB, HOUSE_DB...) with specified values for MATRIX, but that seems like
a lot of work and not very objectoriented.
I�ve read the GNAT RM about the problem (Ada95 <-> Ada83) "Indefinite
subtypes in generics" but don`t seem to understand, especially when there�s
a standard package involved.

All you experienced ones out there leave the "Ada is dead"-discussions and
pleaseeeeee help me out...

Magnus Sparf
magnus-s@dsv.su.se