Re: Direct_IO problem -- generic package problem

["nicolas" <n.brunot@cadwin.com>]

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But that means that you cannot use the predefined generic package Direct_IO
any more ...
With the given code, the pragma Ada_83 is the simplest solution I see which
doesn't require code rewriting..
In most similar cases I met, if everything worked well in Ada83, this pragma
allows you to compile and run in Ada95.
If this works, and if there is a strong deadline for a usable version of the
software, delaying the rewriting of the implementation is not necesseraly a
bad option.

Of course, it would be much better to rewrite the implementation without
Direct_IO, or with another IO implementation, if you can afford it.
Direct_IO can be compiler specific (unfortunately pragma Ada_83 is compiler
specific too ...)

"David C. Hoos, Sr." <david.c.hoos.sr@ada95.com> a �crit dans le message
news: mailman.994937958.12891.comp.lang.ada@ada.eu.org...
> I don't believe the gnat pragma will help in this situation, because
> the restriction is on Ada95 that was not in Ada83.  The real
> solution is to fix the code which is very simple to do, viz.:
>
> This sounds like the restriction that was put on generic formal type
> declarations with no discriminant part that they be instantiated
> only with definite subtypes
>
> If the generic is to be instantiated with indefinite subtypes, then the
> formal type declaration of the generic must include the unknown
> discriminant part (<>).
>
> For example, if the declaration of Element_Type is
>
>     type Element_Type is private;
>
> then changing the declaration to
>
>     type Element_Type (<>) is private;
>
> will allow (but not require) instantiation to be with indefinite
> types.
>
> This is discussed in section 31. of the document found at
> http://www.adaic.org/docs/compat-guide/compat-guide6-0.txt
>
> This document deals with the other Ada83/Ada95 compatibility
> issues, as well.
>
> ----- Original Message -----
> From: "nicolas" <n.brunot@cadwin.com>
> Newsgroups: comp.lang.ada
> To: <comp.lang.ada@ada.eu.org>
> Sent: July 12, 2001 4:19 AM
> Subject: Re: Direct_IO problem -- generic package problem
>
>
> > If you are using gnat, you can add
> > pragma Ada_83;
> > in this body to enforce Ada_83 restrictions (provided you don't use
specific
> > Ada95 features in this body)
> > But this is really a bug of Ada83 cerrected in Ada95
> > Nicolas
> >
> > "Magnus Sparf" <magnus-s@dsv.su.se> a �crit dans le message news:
> > 9ijobe$qb4$1@mercur.foa.se...
> > > 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
> > >
> > >
> > >
> >
> >
> > _______________________________________________
> > comp.lang.ada mailing list
> > comp.lang.ada@ada.eu.org
> > http://ada.eu.org/mailman/listinfo/comp.lang.ada
> >
>