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From: eachus@spectre.mitre.org (Robert I. Eachus)
Subject: Re: Invoking parental methods (was: Java vs Ada 95)
Date: 1996/11/08
Date: 1996-11-08T00:00:00+00:00	[thread overview]
Message-ID: <EACHUS.96Nov8183418@spectre.mitre.org> (raw)
In-Reply-To: E0EIM2.A3p.0.-s@inmet.camb.inmet.com


In article <55tm4r$8al@news.ida.org> wheeler@aphrodite (David Wheeler) writes:

  > I actually recommended such an attribute (I named it 'Parent) as
  > part of the Ada95 revision. My suggestion was struck down for the
  > reason you see here (you can emulate it with "subtype").  I still
  > think it's a good idea, even though there's a simple workaround,
  > because it simplifies maintenance and reduces possible errors
  > (e.g. forgetting to redefine subtype Parent when the hieararchy
  > changes).

   Once upon a time in Ada 9X you could emulate it fairly easily, if
you knew the name of the parent.  But with the current (and very
correct) rules on dispatching, it can be VERY difficult to get the
effect you want.  (A view conversion to the parent type that
dispatches dynamically or statically depending on context.)  I argued
for the attribute at more than one WG9 workshop, and got regularly put
aside with "it is easy" to emulate.  Now we have the rules for
dispatching right but it can be very hard to get the dynamic behavior
to work.

    I guess most people thought about the static case, and didn't
realize that there are cases where you want the dynamic behavior.  For
example, suppose I want to find out how deep an inheritance is.

    I want to write:

       function Count_Depth(Bar: in Foo'CLASS) return Integer is
       begin
         if Foo'Tag = Bar'Tag then return 0;
         else return Count_Depth(Parent(Bar)) + 1; end if;
       end Count_Depth;

    This is a semi-silly example, but think about a typical window
system where I want to add gadgets by inheritance.  Most of the time,
the behavior of the child statically calling the parent's method is
fine, but often you want to walk the inheritance list, doing something
at each level.  You either define all these methods on the root class,
which requires an impossible amount of forethough since you didn't
write that package, or you make them classwide, and need the dynamic
behavior.

--

					Robert I. Eachus

with Standard_Disclaimer;
use  Standard_Disclaimer;
function Message (Text: in Clever_Ideas) return Better_Ideas is...




  parent reply	other threads:[~1996-11-08  0:00 UTC|newest]

Thread overview: 250+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
1996-10-08  0:00 Once again, Ada absent from DoD SBIR solicitation Gregory Aharonian
1996-10-08  0:00 ` Gandalf
1996-10-09  0:00 ` Bill Nielsen
1996-10-09  0:00   ` Stanley R. Allen
1996-10-09  0:00     ` C++ Standardization (was: Once again, Ada absent from DoD SBIR solicitation) David Shochat
1996-10-10  0:00       ` Robert Dewar
1996-10-10  0:00         ` David Shochat
1996-10-20  0:00           ` Richard Riehle
1996-10-20  0:00             ` nasser
1996-10-21  0:00               ` Shayne Flint
1996-10-21  0:00                 ` Robert A Duff
1996-10-21  0:00                   ` Robert Dewar
1996-10-22  0:00                   ` Shayne Flint
1996-10-22  0:00                     ` Robert A Duff
1996-10-22  0:00                   ` Ken Garlington
1996-10-22  0:00               ` Rush Kester
1996-10-11  0:00         ` Ed Falis
1996-10-11  0:00           ` Robert Dewar
1996-10-12  0:00             ` Kevin D. Heatwole
1996-10-12  0:00               ` Robert Dewar
1996-10-13  0:00                 ` Larry Kilgallen
1996-10-13  0:00             ` Ed Falis
1996-10-11  0:00       ` Dave Wood
1996-10-11  0:00         ` Dave Wood
1996-10-17  0:00         ` Garbage Collection in Ada Thomas Kendelbacher
1996-10-10  0:00     ` Once again, Ada absent from DoD SBIR solicitation Mike Stark
1996-10-10  0:00       ` Stanley R. Allen
1996-10-11  0:00         ` Mitch Gart
1996-10-11  0:00           ` Ken Garlington
1996-10-11  0:00           ` Robert Dewar
1996-10-14  0:00             ` Mitch Gart
1996-10-14  0:00               ` Ken Garlington
1996-10-14  0:00           ` Norman H. Cohen
1996-10-14  0:00             ` Bevin R. Brett
1996-10-10  0:00     ` Mitch Gart
1996-10-10  0:00       ` Java vs Ada 95 (Was Re: Once again, Ada absent from DoD SBIR solicitation) Brian Rogoff
1996-10-10  0:00         ` Dave
1996-10-11  0:00           ` Stephen Leake
1996-10-11  0:00             ` Dave
1996-10-11  0:00               ` Robert Dewar
1996-10-12  0:00                 ` Dave
1996-10-12  0:00                   ` Robert Dewar
1996-10-14  0:00                   ` Keith Thompson
1996-10-11  0:00           ` Tucker Taft
1996-10-14  0:00             ` Brian Rogoff
1996-10-15  0:00               ` Mitch Gart
1996-10-15  0:00                 ` Larry Kilgallen
1996-10-15  0:00                   ` Mark A Biggar
1996-10-16  0:00                 ` Brian Rogoff
1996-10-28  0:00                 ` Kenneth Almquist
1996-10-29  0:00                   ` Invoking parental methods (was: Java vs Ada 95) Larry Kilgallen
1996-10-31  0:00                     ` Kenneth Almquist
1996-10-31  0:00                       ` Larry Kilgallen
1996-11-05  0:00                         ` Mitch Gart
1996-11-05  0:00                           ` Larry Kilgallen
1996-11-09  0:00                             ` Joel VanLaven
1996-11-05  0:00                           ` Tucker Taft
1996-11-05  0:00                             ` Larry Kilgallen
1996-11-06  0:00                               ` Robert A Duff
1996-11-06  0:00                                 ` Larry Kilgallen
1996-11-06  0:00                             ` Robert I. Eachus
1996-11-07  0:00                               ` David Wheeler
1996-11-06  0:00                             ` Mitch Gart
1996-11-08  0:00                             ` Jon S Anthony
1996-11-08  0:00                             ` Robert I. Eachus [this message]
1996-10-15  0:00               ` Java vs Ada 95 (Was Re: Once again, Ada absent from DoD SBIR solicitation) Robert A Duff
1996-10-15  0:00                 ` Portability of Arithmetic (was: Java vs Ada 95) Larry Kilgallen
1996-10-16  0:00                   ` Robert A Duff
1996-10-16  0:00                     ` Robert Dewar
1996-10-17  0:00                       ` Robert A Duff
1996-10-17  0:00                         ` Robert Dewar
1996-10-18  0:00                           ` Norman H. Cohen
1996-10-18  0:00                             ` Robert Dewar
1996-10-18  0:00                               ` Brian R. Hanson
1996-10-19  0:00                                 ` Robert Dewar
1996-10-19  0:00                                   ` Larry Kilgallen
1996-10-22  0:00                                     ` Once again, Ada absent from DoD SBIR solicitation Dale Stanbrough
1996-10-27  0:00                                       ` Robert Dewar
1996-10-21  0:00                                   ` Portability of Arithmetic (was: Java vs Ada 95) Norman H. Cohen
1996-10-21  0:00                                     ` Robert Dewar
1996-10-21  0:00                               ` Lance Kibblewhite
1996-10-21  0:00                               ` Norman H. Cohen
1996-10-21  0:00                                 ` Robert Dewar
1996-10-22  0:00                                   ` Larry Kilgallen
1996-10-23  0:00                                     ` Robert Dewar
1996-10-23  0:00                                       ` Larry Kilgallen
1996-10-23  0:00                                   ` Norman H. Cohen
1996-10-18  0:00                           ` Larry Kilgallen
1996-10-18  0:00                             ` Robert A Duff
1996-10-17  0:00                         ` Larry Kilgallen
1996-10-18  0:00                           ` Robert A Duff
1996-10-17  0:00                     ` Stephen Leake
1996-10-17  0:00                       ` Robert A Duff
1996-10-17  0:00                         ` Larry Kilgallen
1996-10-18  0:00                           ` Robert A Duff
1996-10-17  0:00                         ` Robert Dewar
1996-10-15  0:00                 ` Java vs Ada 95 (Was Re: Once again, Ada absent from DoD SBIR solicitation) Robert Dewar
1996-10-17  0:00                 ` Alan Brain
1996-10-17  0:00                   ` Robert Dewar
1996-10-17  0:00                   ` Robert A Duff
1996-10-18  0:00                   ` Keith Thompson
1996-10-20  0:00                     ` Alan Brain
1996-10-24  0:00                 ` Robert I. Eachus
1996-10-15  0:00               ` Mike Stark
1996-10-15  0:00                 ` Robert Dewar
1996-10-16  0:00                   ` Mike Stark
1996-10-17  0:00                     ` Robert A Duff
1996-10-17  0:00                 ` Why no Propagates? Matthew Heaney
1996-10-18  0:00                   ` Robert A Duff
1996-10-18  0:00                   ` Norman H. Cohen
1996-10-18  0:00                     ` Robert Dewar
1996-10-18  0:00                   ` Robert Dewar
1996-10-16  0:00             ` Java vs Ada 95 (Was Re: Once again, Ada absent from DoD SBIR solicitation) Jon S Anthony
1996-10-16  0:00             ` Brian Rogoff
1996-10-16  0:00             ` Brian Rogoff
1996-10-16  0:00               ` Robert Dewar
1996-10-17  0:00                 ` Robert A Duff
1996-10-17  0:00                   ` Robert Dewar
1996-11-22  0:00                 ` Van Snyder
1996-11-25  0:00                   ` Java vs Ada vs Inferno, floating point arithmetic Anssi Porttikivi
1996-10-11  0:00           ` Java vs Ada 95 (Was Re: Once again, Ada absent from DoD SBIR solicitation) Robert Dewar
1996-10-12  0:00             ` davedave
1996-10-12  0:00               ` Robert Dewar
1996-10-13  0:00               ` Larry Kilgallen
1996-10-18  0:00           ` Why no Propagates? Michel Gauthier
1996-10-22  0:00             ` Richard A. O'Keefe
1996-10-23  0:00           ` Michel Gauthier
1996-10-11  0:00         ` Java vs Ada 95 (Was Re: Once again, Ada absent from DoD SBIR solicitation) Mitch Gart
1996-10-11  0:00       ` Jon S Anthony
1996-10-11  0:00       ` Jon S Anthony
1996-10-12  0:00         ` Robert Dewar
1996-10-14  0:00           ` Mitch Gart
1996-10-14  0:00           ` Brian R. Hanson
1996-10-14  0:00         ` Keith Thompson
1996-10-15  0:00           ` Dale Stanbrough
1996-10-15  0:00             ` Brian R. Hanson
1996-10-20  0:00           ` nasser
1996-10-12  0:00       ` davedave
1996-10-12  0:00         ` Robert Dewar
1996-10-16  0:00           ` Jon S Anthony
1996-10-16  0:00           ` Jon S Anthony
1996-10-14  0:00       ` Brian Rogoff
1996-10-14  0:00       ` Jon S Anthony
1996-10-14  0:00       ` Jon S Anthony
1996-10-14  0:00       ` Jon S Anthony
1996-10-14  0:00       ` Jon S Anthony
1996-10-14  0:00         ` Robert Dewar
1996-10-15  0:00           ` Robert A Duff
1996-10-15  0:00             ` Larry Kilgallen
1996-10-16  0:00               ` Lars Farm
1996-10-16  0:00                 ` Robert Dewar
1996-10-17  0:00           ` Why no Free? Matthew Heaney
1996-10-18  0:00             ` John Herro
1996-10-19  0:00               ` John Herro
1996-10-18  0:00             ` Robert A Duff
1996-10-18  0:00             ` Robert Dewar
1996-10-15  0:00       ` Java vs Ada 95 (Was Re: Once again, Ada absent from DoD SBIR solicitation) Robert I. Eachus
1996-10-15  0:00         ` Robert Dewar
1996-10-15  0:00       ` Robert I. Eachus
1996-10-15  0:00       ` Brian Rogoff
1996-10-16  0:00       ` Jon S Anthony
1996-10-16  0:00       ` Jon S Anthony
1996-10-16  0:00       ` Jon S Anthony
1996-10-16  0:00       ` Samuel T. Harris
1996-10-16  0:00       ` Jon S Anthony
1996-10-18  0:00         ` Keith Thompson
1996-10-16  0:00       ` Jon S Anthony
1996-10-17  0:00         ` Robert Dewar
1996-10-17  0:00         ` Robert Dewar
1996-10-18  0:00       ` Jon S Anthony
1996-10-18  0:00       ` Jon S Anthony
1996-10-18  0:00       ` Jon S Anthony
1996-10-29  0:00       ` Kenneth Almquist
1996-10-29  0:00         ` Robert Dewar
1996-10-31  0:00           ` Kenneth Almquist
1996-10-29  0:00       ` Jon S Anthony
1996-10-29  0:00       ` Robert I. Eachus
1996-10-30  0:00       ` Stephen Leake
1996-10-31  0:00         ` Lars Farm
1996-10-31  0:00       ` Kenneth Almquist
1996-10-31  0:00       ` Jon S Anthony
1996-11-01  0:00       ` Robert I. Eachus
1996-11-01  0:00         ` Robert A Duff
     [not found]           ` <55gkch$gg6@fozzie.sun3.iaf.nl>
1996-11-03  0:00             ` Robert A Duff
1996-11-03  0:00               ` Robert Dewar
1996-11-04  0:00                 ` Larry Kilgallen
1996-11-04  0:00                   ` Robert Dewar
1996-11-05  0:00                 ` Fast locking (Was Re: Java vs Ada 95) Geert Bosch
1996-11-06  0:00                   ` Larry Kilgallen
1996-11-06  0:00                     ` Robert Dewar
1996-11-06  0:00                     ` Geert Bosch
1996-11-07  0:00                       ` Larry Kilgallen
1996-11-07  0:00                         ` Robert Dewar
1996-11-11  0:00                           ` Norman H. Cohen
1996-11-08  0:00                         ` Geert Bosch
1996-11-02  0:00         ` Java vs Ada 95 (Was Re: Once again, Ada absent from DoD SBIR solicitation) Robert Dewar
1996-11-04  0:00         ` Robert I. Eachus
1996-11-05  0:00           ` Larry Kilgallen
1996-11-14  0:00           ` Robert Dewar
1996-11-16  0:00             ` Geert Bosch
1996-11-17  0:00               ` Robert Dewar
1996-11-17  0:00                 ` Robert A Duff
1996-11-18  0:00                   ` Robert Dewar
1996-11-19  0:00                     ` Robert A Duff
1996-11-18  0:00                 ` Norman H. Cohen
1996-11-18  0:00                 ` Geert Bosch
1996-11-22  0:00                   ` Robert Dewar
1996-11-16  0:00             ` Robert A Duff
1996-11-16  0:00               ` Robert Dewar
1996-11-17  0:00                 ` Unbounded strings (Was: Java vs Ada 95 (Was Re: Once again, Ada absent from DoD SBIR solicitation)) Robert A Duff
1996-11-18  0:00                   ` Robert Dewar
1996-11-19  0:00                     ` Robert A Duff
1996-11-23  0:00                       ` Robert Dewar
1996-11-24  0:00                         ` Robert A Duff
1996-11-25  0:00                         ` Norman H. Cohen
1996-11-27  0:00                           ` Robert Dewar
1996-11-19  0:00                     ` Joel VanLaven
1996-11-23  0:00                       ` Robert Dewar
1996-11-21  0:00                   ` Robert I. Eachus
1996-11-24  0:00                     ` Robert Dewar
1996-11-24  0:00                       ` Fergus Henderson
1996-11-24  0:00                         ` Robert Dewar
1996-11-25  0:00                       ` Kevin D. Heatwole
1996-11-25  0:00                         ` Robert A Duff
1996-11-26  0:00                           ` Kevin D. Heatwole
1996-11-26  0:00                             ` Robert A Duff
1996-11-26  0:00                               ` Larry Kilgallen
1996-11-27  0:00                               ` Robert Dewar
1996-11-27  0:00                               ` Norman H. Cohen
1996-11-29  0:00                                 ` Robert A Duff
1996-11-29  0:00                                 ` Fergus Henderson
1996-11-26  0:00                         ` Geert Bosch
1996-11-26  0:00                           ` Robert Dewar
1996-11-25  0:00                   ` Robert I. Eachus
1996-11-20  0:00                 ` Jon S Anthony
1996-11-24  0:00                   ` Robert Dewar
1996-11-06  0:00         ` Java vs Ada 95 (Was Re: Once again, Ada absent from DoD SBIR solicitation) Robert I. Eachus
1996-10-11  0:00     ` Ada and the DoD HLA (was: " John Cosby
1996-10-13  0:00     ` Java vs Ada 95 (Was " Hannes Haug
1996-11-03  0:00     ` Hannes Haug
1996-11-06  0:00     ` Fast locking (Was Re: Java vs Ada 95) Hannes Haug
1996-11-06  0:00     ` Hannes Haug
1996-10-11  0:00   ` Once again, Ada absent from DoD SBIR solicitation Matthew M. Lih
1996-10-18  0:00     ` Rush Kester
1996-10-21  0:00   ` C++ Standardization (was: Once again, Ada absent from DoD SBIR solicitation) David Emery
1996-10-10  0:00 ` Jon S Anthony
1996-10-11  0:00 ` Jon S Anthony
1996-10-22  0:00 ` Tarjei Jensen
1996-10-22  0:00   ` C++ Standardization (was: Once again, Ian Ward
1996-11-01  0:00 ` Java vs Ada 95 (Was Re: Once again, Ada absent from DoD SBIR solicitation) Jon S Anthony
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