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From: dewar@cs.nyu.edu (Robert Dewar)
Subject: Re: Two ideas for the next Ada standard
Date: 1996/09/03
Message-ID: <dewar.841755298@schonberg>#1/1
X-Deja-AN: 178176143
references: <5009h5$ir4@netline-fddi.jpl.nasa.gov>
 	<503sbo$j45@goanna.cs.rmit.edu.au> <DwyFuC.E0K@world.std.com>
 	<507akg$t9u@krusty.irvine.com> <Dx05yF.Jpo@world.std.com>
 	<ws9bufo7kle.fsf@schonberg.cs.nyu.edu> <dewar.841702553@schonberg>
 <ws93f10kxcy.fsf@schonberg.cs.nyu.edu>
organization: Courant Institute of Mathematical Sciences
newsgroups: comp.lang.ada
Date: 1996-09-03T00:00:00+00:00
List-Id: <comp.lang.ada>


Laurent said

"   I was refering to the fact that in Ada 83, put aside efficiency
issues, you could have completly removed the notion of private part,
and put everything in the body without changing (too much) the
language, since nothing can gain visibility to the body (or to the
private part), so this private part could be considered as part of the
body.
"

OK, that makes sense. I had not realized that you (and Bob?) were suggesting
completely removing the notion of private part in Ada 83. I agree that is
technically sensible, but I find the notion of a private part useful from
an abstraction point of view in any case, even discounting your quite
correct observation that the private part plays an important new role
in Ada 95.

In fact in Ada 95, one of the things I found took some learning was that
private parts do indeed play a completely different role. If you simply
think of private parts as completing private stuff in the spec, and
then you see that child packages have access to this, that's interesting,
but misses a very important and powerful aspect of Ada 95 that has no
analog in Ada 83.

In Ada 95, it makes sense to put all sorts of stuff in private parts,
including types and subprograms that have nothing directly to do with
what is in the spec. You can even imagine an empty spec with a big
private part. The reason that all this stuff is in a private part is
to limit visibility to clients and permit visibility only to children.

For example, the official spec of package Ada is empty, but it is quite
reasonable for an implementation to add a private part to this package
that contains stuff needed by children of Ada in a particular
implementation. The same is true for System. GNAT does not do this,
but probably it should ...