From: Adam Beneschan <adam@irvine.com>
Subject: Re: Rational for not making cursor tagged in Containers
Date: 24 Apr 2007 09:27:37 -0700
Date: 2007-04-24T09:27:37-07:00 [thread overview]
Message-ID: <1177432057.705889.229690@n35g2000prd.googlegroups.com> (raw)
In-Reply-To: <1ccueevyp8oba.11c8wwyujtw1o$.dlg@40tude.net>
On Apr 24, 3:43 am, "Dmitry A. Kazakov" <mail...@dmitry-kazakov.de>
wrote:
> >>> X, Y : GUI_Boolean;
>
> >>> If you say X = Y, does it compare just the values, or does it compare
> >>> the discriminants also?
>
> >> That depends on how equality operation were defined for the given type. In
> >> the concrete case of GUI_Boolean, the user-defined "=" would raise
> >> Constraint_Error if at least one of the discriminants is false.
>
> > OK, I've got it.
>
> > function "=" (X, Y : GUI_Boolean) return Boolean is
> > begin
> > if not X.Defined or else not Y.Defined then
> > raise Constraint_Error;
> > else
> > return X = Y;
> > end if;
> > end "=";
>
> > Is that how you thought this user-defined "=" would be written?
>
> Yup, the predefined "=" should be renamed first.
So a user-defined "=" that causes a stack overflow due to infinite
recursion doesn't bother you?
You still don't see the issue, do you?
> > I think you've missed the point. If you want a feature like this in
> > the language, you can't base the whole semantics on one particular
> > example you happened to come up with (or that you happened to run
> > across a use for when you were working on some particular project).
> > The design of the feature in the language has to be more general than
> > that, and it has to include cases where a discriminant has some
> > meaning other than "This value is defined".
>
> I don't see any problems with generation of a predefined "=" and literals
> (True, False). [True is a literal of the type GUI_Boolean, with all
> consequences of that.]
If True has type GUI_Boolean, then it must have a "Defined"
discriminant. What is True.Defined? How does the programmer indicate
what it would be? (And if you say that True.Defined is "true" because
"true" is a defined value, then you still don't get it---the Ada
language isn't going to know that, and you're going to need a way to
tell it that.)
> > and as one of my examples hinted at, I don't think the
> > current language syntax is enough to handle this without some pretty
> > major surgery.
>
> I don't see any problem with that.
Sure you don't, because you're not the one who'd have to do the
surgery.
-- Adam
next prev parent reply other threads:[~2007-04-24 16:27 UTC|newest]
Thread overview: 66+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-04-19 16:05 Rational for not making cursor tagged in Containers Anh Vo
2007-04-19 18:25 ` Robert A Duff
2007-04-19 19:28 ` Anh Vo
2007-04-19 20:45 ` Robert A Duff
2007-04-19 21:43 ` Dmitry A. Kazakov
2007-04-19 23:59 ` Ray Blaak
2007-04-20 7:54 ` Dmitry A. Kazakov
2007-04-20 10:56 ` Georg Bauhaus
2007-04-20 10:39 ` Dmitry A. Kazakov
2007-04-20 14:42 ` Georg Bauhaus
2007-04-20 14:45 ` Georg Bauhaus
2007-04-20 15:13 ` Dmitry A. Kazakov
2007-04-20 19:37 ` Georg Bauhaus
2007-04-20 19:32 ` Dmitry A. Kazakov
2007-04-20 20:59 ` Robert A Duff
2007-04-20 22:14 ` Dmitry A. Kazakov
2007-04-23 17:38 ` Adam Beneschan
2007-04-23 19:18 ` Dmitry A. Kazakov
2007-04-24 0:15 ` Adam Beneschan
2007-04-24 10:43 ` Dmitry A. Kazakov
2007-04-24 16:27 ` Adam Beneschan [this message]
2007-04-24 20:19 ` Dmitry A. Kazakov
2007-04-26 0:58 ` Adam Beneschan
2007-04-26 7:50 ` Dmitry A. Kazakov
2007-04-26 8:09 ` Markus E Leypold
2007-04-27 8:46 ` Dmitry A. Kazakov
2007-04-27 11:37 ` Markus E Leypold
2007-04-28 17:35 ` Dmitry A. Kazakov
2007-04-29 2:31 ` Randy Brukardt
2007-04-29 8:45 ` Dmitry A. Kazakov
2007-04-27 20:44 ` Robert A Duff
2007-04-26 8:33 ` Markus E Leypold
2007-04-26 11:09 ` Markus E Leypold
2007-04-20 19:55 ` Randy Brukardt
2007-04-22 9:54 ` Georg Bauhaus
2007-04-22 11:19 ` Dmitry A. Kazakov
2007-04-20 20:44 ` Robert A Duff
2007-04-21 5:38 ` Randy Brukardt
2007-04-22 1:14 ` Robert A Duff
2007-04-22 4:08 ` Randy Brukardt
2007-04-20 20:11 ` Randy Brukardt
2007-04-20 21:28 ` Dmitry A. Kazakov
2007-04-21 5:33 ` Randy Brukardt
2007-04-21 9:39 ` Dmitry A. Kazakov
2007-04-22 4:28 ` Randy Brukardt
2007-04-22 8:38 ` Dmitry A. Kazakov
2007-04-23 23:26 ` Randy Brukardt
2007-04-24 10:43 ` Dmitry A. Kazakov
2007-04-24 8:58 ` Georg Bauhaus
2007-04-24 12:21 ` Dmitry A. Kazakov
2007-04-21 4:48 ` unifying arrays and records (was Re: Rational for not making cursor tagged in Containers) Ray Blaak
2007-04-20 17:05 ` Rational for not making cursor tagged in Containers Ray Blaak
2007-04-20 18:46 ` Dmitry A. Kazakov
2007-04-20 18:52 ` Ray Blaak
2007-04-20 19:54 ` Robert A Duff
2007-04-20 1:18 ` Anh Vo
2007-04-20 7:53 ` Dmitry A. Kazakov
2007-04-20 9:26 ` Maciej Sobczak
2007-04-20 10:15 ` Dmitry A. Kazakov
2007-04-20 11:59 ` Jean-Pierre Rosen
2007-04-20 13:23 ` Anh Vo
2007-04-20 16:02 ` Jean-Pierre Rosen
2007-04-21 2:53 ` Anh Vo
2007-04-20 3:03 ` Randy Brukardt
2007-04-20 2:53 ` Randy Brukardt
2007-04-20 16:08 ` Anh Vo
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