LISTSERV mailing list manager LISTSERV 16.0

Help for TEAM-ADA Archives


TEAM-ADA Archives

TEAM-ADA Archives


TEAM-ADA@LISTSERV.ACM.ORG


View:

Message:

[

First

|

Previous

|

Next

|

Last

]

By Topic:

[

First

|

Previous

|

Next

|

Last

]

By Author:

[

First

|

Previous

|

Next

|

Last

]

Font:

Proportional Font

LISTSERV Archives

LISTSERV Archives

TEAM-ADA Home

TEAM-ADA Home

TEAM-ADA  February 1999

TEAM-ADA February 1999

Subject:

Re: Unconstrained Arrays problem

From:

Rick Duley <[log in to unmask]>

Reply-To:

[log in to unmask]

Date:

Fri, 5 Feb 1999 12:17:29 +0800

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (157 lines)

        I received suggestions from Ben Brosgol, Steven Deller, David Hoos Sr, Sam
Mize and Richard Riehle. Thanks folks for your rapid and helpful responses
to my query.

1.      On the matter of declaration of Unconstrained Arrays as 'limited
private' there are two schools of thought:

        Ben Brosgol reported:

You can declare a private type with an "unknown discriminant part".  The
following example compiles and runs (I tried it under Aonix ObjectAda
7.1.2):
---
package P is
    type T(<>) is private;
    function F(N : Integer) return T;
private
    type T is array(Positive range <>) of Integer;
end P;

package body P is
    function F(N : Integer) return T is
    begin
        return T'(1..N => 0);
    end F;
end P;

with P; use P;
procedure Test_Unconstrained is
    X : T := F(10);
begin
    null;
end Test_Unconstrained;

        and yet Steven Deller's response was:

For item 1, my compiler tells me that for the following:

package Trial3 is
    type Case_Type is (Open, Shut);
    type Uncon is private;
    procedure Dumb (X : in out Uncon);
private
    type Uncon is array (Positive range <>) of Case_Type;
end Trial3;

" >>> Line 6: type Uncon is array (Positive range <>) of Case_Type"
"*** array (Positive range <>) of Case_Type must be constrained [RM_95
7.3(12)]"   -- oops! missed that! :(

When I read 7.3(12) it states that "..., then the full_type_declaration
shall
define a definite subtype" (and a definite subtype requires array bounds).
 That makes sense to me, since if code that used this package declared an
object of type Uncon, there would be no way to determine the array bounds
for
that object.

It is possible to use access types for Uncon, such that only the package
body
does any actual allocations of array entities, which may satisfy the
original
need you had:

package Trial2 is
    type Case_Type is (Open, Shut);
    type Uncon is private;
private
    type Uncon_array is array (Positive range <>) of Case_Type;
    type Uncon is access Uncon_array ;
end Trial2;

It is also possible to defer the definition of the Uncon_array into the
body
of the package:

package Trial2 is
    type Case_Type is (Open, Shut);
    type Uncon is private;
    procedure Dumb (X : in out Uncon);
private
    type Uncon_Array;
    type Uncon is access Uncon_Array;
end Trial2;

package body Trial2 is
    type Uncon_Array is array (Positive range <>) of Case_Type;
    procedure Dumb (X : in out Uncon) is
    begin
        if X = null then
            X := new Uncon_Array'(1 => Open, 2 => Shut);
        end if;
    end Dumb;
end Trial2;


2.      Declaration of a constant: There were two main variations on solutions.

        Always_Guilty : constant Court_Type := (2 .. 1 => Shut);

        as David Hoos commented "You have to specify a value for the array
elements that aren't going to be there!"

        Alternatively, as Sam Mize suggested: "...you can just declare it as a
variable.  After all, it's effectively constant -- you can't change any of
the (non-existent) values!

        Never_Guilty: Court_Type (2..1);

        Richard Riehle made the point: "..., good
object-oriented programming style would suggest that we abandon the
use of deferred constants in our package designs.  The usual form is
something such as,

      package P is
          type T is private;
          Empty_T : constant T;
          -- more public stuff
      private
          full definitions of private stuff
      end P;

        "The more object-oriented way to approach this is to export a function
for Empty_T in place of the deferred constant.

             function Empty_T return T;

        "This allows a variety of implementations on Empty_T, eliminates problems
of dependencies when we change the values of the constants later, and
improves maintainability.  It also eliminates the need for the designer
to fool around with syntax better left to the package implementor."

        It seems there _are_ ways around the matter.  Once again, thanks to all!

-----------------------------------------------------------------------
                                    ______
Rick Duley                         /      \
Edith Cowan University            (____/\  )
Perth, Western Australia           |___  U?(____
                                   _\L.   |      \     ___
ECU: +61 (08) 9370 6619          / /"""\ /.-'     |   |\  |
mob: 0416 365 619               ( /  _/u     |    \___|_)_|
                                 \|  \\      /   / \_(___ __)
                                  |   \\    /   /  |  |    |
                                  |    )  _/   /   )  |    |
                                  _\__/.-'    /___(   |    |
I think,                       _/  __________/     \  |    |
Therefore I am...             //  /  (              ) |    |
                             ( \__|___\    \______ /__|____|
I Think!                              \    (___\   |______)_/
                               \   |\   \  \     /
                                \  | \__ )  )___/
                                 \  \  )/  /__(
                                  ___ |  /_//___|   \_________
                               _/  ( / OUuuu    \
                              `----'(____________)

Top of Message | Previous Page | Permalink

Advanced Options


Options

Log In

Log In

Get Password

Get Password


Search Archives

Search Archives


Subscribe or Unsubscribe

Subscribe or Unsubscribe


Archives

December 2017
November 2017
October 2017
September 2017
June 2017
May 2017
April 2017
January 2017
December 2016
November 2016
October 2016
August 2016
July 2016
June 2016
May 2016
April 2016
March 2016
February 2016
January 2016
December 2015
November 2015
October 2015
September 2015
August 2015
June 2015
May 2015
April 2015
March 2015
February 2015
January 2015
December 2014
November 2014
September 2014
August 2014
July 2014
June 2014
May 2014
April 2014
March 2014
February 2014
January 2014
December 2013
November 2013
October 2013
September 2013
June 2013
May 2013
April 2013
March 2013
February 2013
January 2013
December 2012
November 2012
October 2012
September 2012
August 2012
July 2012
June 2012
May 2012
April 2012
February 2012
January 2012
December 2011
November 2011
October 2011
September 2011
August 2011
July 2011
June 2011
May 2011
April 2011
December 2010
November 2010
October 2010
September 2010
June 2010
May 2010
April 2010
March 2010
February 2010
January 2010
December 2009
November 2009
October 2009
September 2009
August 2009
July 2009
June 2009
May 2009
April 2009
February 2009
January 2009
December 2008
November 2008
October 2008
September 2008
August 2008
June 2008
May 2008
April 2008
March 2008
February 2008
January 2008
December 2007
November 2007
October 2007
September 2007
June 2007
May 2007
March 2007
February 2007
December 2006
November 2006
October 2006
September 2006
August 2006
July 2006
June 2006
May 2006
April 2006
March 2006
February 2006
January 2006
December 2005
November 2005
October 2005
August 2005
July 2005
June 2005
May 2005
April 2005
March 2005
February 2005
January 2005
December 2004
November 2004
October 2004
September 2004
August 2004
July 2004
June 2004
May 2004
March 2004
February 2004
January 2004
December 2003
November 2003
October 2003
September 2003
August 2003
July 2003
June 2003
May 2003
April 2003
March 2003
February 2003
January 2003
December 2002
November 2002
October 2002
September 2002
August 2002
July 2002
June 2002
May 2002
April 2002
March 2002
February 2002
December 2001
November 2001
October 2001
September 2001
August 2001
July 2001
June 2001
May 2001
April 2001
March 2001
February 2001
January 2001
December 2000
November 2000
October 2000
September 2000
August 2000
July 2000
June 2000
May 2000
April 2000
March 2000
February 2000
January 2000
December 1999
November 1999
October 1999
September 1999
August 1999
July 1999
June 1999
May 1999
April 1999
March 1999
February 1999
January 1999
December 1998
November 1998
October 1998
September 1998
August 1998
July 1998
June 1998
May 1998
April 1998
March 1998
February 1998
January 1998
December 1997
November 1997
October 1997
September 1997
August 1997
July 1997
June 1997
May 1997
April 1997
March 1997
February 1997
January 1997
December 1996
November 1996
October 1996

ATOM RSS1 RSS2



LISTSERV.ACM.ORG

Secured by F-Secure Anti-Virus CataList Email List Search Powered by the LISTSERV Email List Manager