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=-1.9 required=5.0 tests=BAYES_00 autolearn=ham
	autolearn_force=no version=3.4.4
X-Google-Thread: 103376,c80e6f742e73478f
X-Google-NewGroupId: yes
X-Google-Attributes: gida07f3367d7,domainid0,public,usenet
X-Google-Language: ENGLISH,ASCII-7-bit
Path: 
 g2news2.google.com!news1.google.com!npeer02.iad.highwinds-media.com!news.highwinds-media.com!feed-me.highwinds-media.com!nntp.club.cc.cmu.edu!micro-heart-of-gold.mit.edu!newsswitch.lcs.mit.edu!nntp.TheWorld.com!not-for-mail
From: Robert A Duff <bobduff@shell01.TheWorld.com>
Newsgroups: comp.lang.ada
Subject: Re: Ensuring postconditions in the face of exceptions
Date: Mon, 15 Mar 2010 12:44:25 -0400
Organization: The World Public Access UNIX, Brookline, MA
Message-ID: <wccljdtlel2.fsf@shell01.TheWorld.com>
References: 
 <820d96c0-5d67-4b8c-8c5b-811ca4f1127e@g26g2000yqn.googlegroups.com>
 <8990d686-f703-4e9c-91b7-32410289983d@g11g2000yqe.googlegroups.com>
 <87ljdv56gy.fsf@ludovic-brenta.org> <wccfx42vrpd.fsf@shell01.TheWorld.com>
 <22728d81-9ede-4128-ab47-eacec75f6954@r27g2000yqn.googlegroups.com>
NNTP-Posting-Host: shell01.theworld.com
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
X-Trace: pcls4.std.com 1268671455 15025 192.74.137.71 (15 Mar 2010 16:44:15
 GMT)
X-Complaints-To: abuse@TheWorld.com
NNTP-Posting-Date: Mon, 15 Mar 2010 16:44:15 +0000 (UTC)
User-Agent: Gnus/5.1008 (Gnus v5.10.8) Emacs/21.3 (irix)
Cancel-Lock: sha1:n6ByNwe02bYe7quMygOFj4mnSZQ=
Xref: g2news2.google.com comp.lang.ada:10547
Date: 2010-03-15T12:44:25-04:00
List-Id: <comp.lang.ada>

Ludovic Brenta <ludovic@ludovic-brenta.org> writes:

> No, Dirty is not a property of the object; the type T is used in
> several places, only some of which (a one-line cache, essentially) has
> a Dirty property.

OK, then Dirty is a property of the cache.  So how about:

    type Cache is limited
        record
            X : T;
            Dirty : Boolean := True;
        end record;
    type Cache_Ref is access all Cache;

and pass a parameter of type Cache_Ref?  (Or perhaps
X could be an access type, and point to the T object.)

You need to pass some sort of pointer, explicitly or implicitly,
because when you raise an exception, the copy-back is skipped.
You said that relying on limitedness to force pass-by-referrence
is confusing -- I agree.  So pass an explicit pointer.

I recommend a named access type, because anonymous access parameters
have dynamic accessibility, which is a tripping hazard, and is
less efficient.

- Bob