From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-0.3 required=5.0 tests=BAYES_00,
	REPLYTO_WITHOUT_TO_CC autolearn=no autolearn_force=no version=3.4.4
X-Google-Thread: a07f3367d7,dbbbb21ed7f581b
X-Google-Attributes: gida07f3367d7,public,usenet
X-Google-NewGroupId: yes
X-Google-Language: ENGLISH,ASCII-7-bit
Path: 
 g2news1.google.com!news3.google.com!proxad.net!feeder1-2.proxad.net!newsfeed.straub-nv.de!uucp.gnuu.de!newsfeed.arcor.de!newsspool1.arcor-online.net!news.arcor.de.POSTED!not-for-mail
From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Operation can be dispatching in only one type
Newsgroups: comp.lang.ada
User-Agent: 40tude_Dialog/2.0.15.1
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Reply-To: mailbox@dmitry-kazakov.de
Organization: cbb software GmbH
References: 
 <025105f2-5571-400e-a66f-ef1c3dc9ef32@g27g2000yqn.googlegroups.com>
   <1nbcfi99y0fkg.1h5ox2lj73okx$.dlg@40tude.net>
 <59acf311-3a4a-4eda-95a3-22272842305e@m16g2000yqc.googlegroups.com>
 <e1p8csy5enz.1ndzb6tlh7ckb$.dlg@40tude.net>
 <wcc1vjqteom.fsf@shell01.TheWorld.com>
 <Pine.LNX.4.64.0911230311040.30588@medsec1.medien.uni-weimar.de>
 <wcc8wdn697e.fsf@shell01.TheWorld.com>
 <4b150869$0$6732$9b4e6d93@newsspool2.arcor-online.net>
 <18vlg095bomhd.8bp1o9yysctg$.dlg@40tude.net>
 <4b152ffe$0$7615$9b4e6d93@newsspool1.arcor-online.net>
 <19nhib6rmun1x$.13vgcbhlh0og9$.dlg@40tude.net>
 <4b1557d0$0$7623$9b4e6d93@newsspool1.arcor-online.net>
 <wof0ewwkyzy0$.13398rnn8cmje$.dlg@40tude.net>
 <4b15bf2b$0$7623$9b4e6d93@newsspool1.arcor-online.net>
 <1jcbtmi5rztyp$.norvlhez9i9$.dlg@40tude.net> <hf7icf$ffm$1@munin.nbi.dk>
 <4b179ffb$0$6591$9b4e6d93@newsspool3.arcor-online.net>
 <hf9gcj$oog$1@munin.nbi.dk>
 <qchmzfxola9n$.1owojhwd91cbc.dlg@40tude.net> <hfchg1$mtd$1@munin.nbi.dk>
Date: Sat, 5 Dec 2009 11:32:11 +0100
Message-ID: <1gcigitaii0u0.1psu2vj52e66g$.dlg@40tude.net>
NNTP-Posting-Date: 05 Dec 2009 11:32:15 CET
NNTP-Posting-Host: 771f73a2.newsspool3.arcor-online.net
X-Trace: 
 DXC=bLjn5oeC>5hFXUDVUnEXQmMcF=Q^Z^V3h4Fo<]lROoRa8kF<OcfhCOkD`X^0b4Z<_j[6LHn;2LCVn[<mhadbfdUkXY]FoC9PQeg68hAcC4]6=b
X-Complaints-To: usenet-abuse@arcor.de
Xref: g2news1.google.com comp.lang.ada:8316
Date: 2009-12-05T11:32:15+01:00
List-Id: <comp.lang.ada>

On Fri, 4 Dec 2009 20:45:19 -0600, Randy Brukardt wrote:

> Writing in Ada 2012 as proposed today 
> (and that might change before it gets standardized):
> 
>      procedure Do_Something (Window : Claw.Basic_Window_Type; ...)
>              with Pre => Is_Valid (Window);

Why not to allow such constraints for subtypes? E.g.

   subtype Valid_Window_Type is Window_Type when Is_Valid;

then simply:

   procedure Do_Something (Window : Valid_Window_Type; ...)

> is surely better because it puts the check in the spec where the caller can 
> see it, rather than in comments that can be ignored. (And it also opens up 
> the possibility of tools/compilers warning when it is *not* true at the 
> point of a call, both potentially eliminating generated code and making 
> error detection earlier.)

Yes, but I do prefer the subtypes as the vehicle, rather than arbitrary
preconditions put here and there on the subprograms. The latter is kind of
weak typing to me.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de