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
Path: 
 g2news2.google.com!news2.google.com!news.glorb.com!news.cse.ohio-state.edu!usenet01.sei.cmu.edu!elk.ncren.net!newsswitch.lcs.mit.edu!nntp.TheWorld.com!not-for-mail
From: Robert A Duff <bobduff@shell01.TheWorld.com>
Newsgroups: comp.lang.ada
Subject: Re: Generic package parameters not externally visible : what's the
  rational ?
Date: Mon, 26 Oct 2009 11:02:48 -0400
Organization: The World Public Access UNIX, Brookline, MA
Message-ID: <wcceioq6vvr.fsf@shell01.TheWorld.com>
References: <d31a3f23-975d-4ae7-954a-82055b50f172@31g2000vbf.googlegroups.com>
 <92abb636-b3a0-429b-b6b4-03b6abe2d206@x15g2000vbr.googlegroups.com>
NNTP-Posting-Host: shell01.theworld.com
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
X-Trace: pcls6.std.com 1256569369 19249 192.74.137.71 (26 Oct 2009 15:02:49
 GMT)
X-Complaints-To: abuse@TheWorld.com
NNTP-Posting-Date: Mon, 26 Oct 2009 15:02:49 +0000 (UTC)
User-Agent: Gnus/5.1008 (Gnus v5.10.8) Emacs/21.3 (irix)
Cancel-Lock: sha1:y+cNqmTIYaUoYm7Ogs13mIlM6r4=
Xref: g2news2.google.com comp.lang.ada:8786
Date: 2009-10-26T11:02:48-04:00
List-Id: <comp.lang.ada>

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

> I think this is at least consistent: the values of subprogram
> parameters are also invisible outside the subprogram. Making "in out"
> generic formal variables visible outside the generic would be
> dangerous IMHO. As for generic formal types, subprograms, packages and
> constants... why not.

I don't buy the analogy with subprograms.  When you "instantiate"
(i.e. call) a subprogram, you don't create a nameable entity
that can be referred to from outside.  A better analogy would
be discriminants, which are really parameters passed in to
a type when you "instantiate" it (i.e. create an object of the type).
And the discriminants are visible from outside the object,
as they should be.

I don't see any particular danger for the "in out" case.
It would mean you can reach in and change it from the outside,
but that's true of regular variables declared in the generic
package spec.  So don't do that.  (It's also true for "in out"s
in the formal package case, if I remember correctly -- I'm
too lazy to look it up right now.)

Anyway, generic formal "in out" parameters are used approximately
never, so I don't care that much if they're slightly dangerous.

- Bob