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-Language: ENGLISH,ASCII-7-bit
X-Google-Thread: 103376,50137bb64a119cfc
X-Google-Attributes: gid103376,public
X-Google-ArrivalTime: 2003-02-10 10:57:04 PST
Path: 
 archiver1.google.com!news1.google.com!newsfeed.stanford.edu!news-spur1.maxwell.syr.edu!news.maxwell.syr.edu!newsfeed.mathworks.com!wn13feed!worldnet.att.net!204.127.198.203!attbi_feed3!attbi.com!sccrnsc04.POSTED!not-for-mail
From: tmoran@acm.org
Newsgroups: comp.lang.ada
Subject: Re: "access constant" discriminant
References: <_TO1a.14664$9y2.6601@nwrddc01.gnilink.net>
X-Newsreader: Tom's custom newsreader
Message-ID: <3CS1a.55972$2H6.1357@sccrnsc04>
NNTP-Posting-Host: 12.234.13.56
X-Complaints-To: abuse@attbi.com
X-Trace: sccrnsc04 1044903423 12.234.13.56 (Mon, 10 Feb 2003 18:57:03 GMT)
NNTP-Posting-Date: Mon, 10 Feb 2003 18:57:03 GMT
Organization: AT&T Broadband
Date: Mon, 10 Feb 2003 18:57:03 GMT
Xref: archiver1.google.com comp.lang.ada:33967
Date: 2003-02-10T18:57:03+00:00
List-Id: <comp.lang.ada>

>What is it that you want to do?
   In the case at hand, I'm using the idiom of a limited controlled type
whose initialization/finalization grabs/releases a resource lock, and the
access discriminant tells which resource.
  type Lock_Type(Resource : access Resource_Type) is new
  Ada.Finalization.Limited_Controlled with ...
and later
  Locker : Lock_Type(Resource'unchecked_access);
  ...
But this won't work when Resource is an "in" parameter, eg a function
parameter.  I suppose Ada is telling me that grabbing a lock is
effectively modifying the resource, and thus something that shouldn't be
done when the resource is an "in" parameter, but the question remains, why
can't one say
  type Lock_Type(Resource : access constant Resource_Type) ...
Did the designers foresee and forestall my use with a function?