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From: val@cs.weber.edu (Val Kartchner)
Newsgroups: comp.lang.ada
Subject: Re: Is Ada the future? [was: Is C++ the future?]
Date: 13 Oct 1994 22:01:25 GMT
Organization: Weber State University, Ogden, Utah
Message-ID: <37kanl$jfd@u.cc.utah.edu>
References: <milodCwwqMy.CK@netcom.com>
 <EACHUS.94Oct3095345@spectre.mitre.org> <milodCx46t7.FIB@netcom.com>
 <1994Oct4.090807@di.epfl.ch>
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Date: 1994-10-13T22:01:25+00:00
List-Id: <comp.lang.ada>

In article <1994Oct4.090807@di.epfl.ch>,
Robb Nebbe <Robb.Nebbe@di.epfl.ch> wrote:
|In my opinion there are two important factors that make software
|maintainable. The ability to define an abstraction and have the
|compiler enforce this abstraction and the ability for the person
|doing the maintenance to understand the abstraction.
|
|For defining and particularly enforcing an abstraction you could
|make a fairly strong case that Ada is better than C++. The case
|wouldn't be that you can't define and enforce an abstraction in
|C++, which would be a bit naive, but that in some cases the effort
|required goes far beyond what is required in Ada.

Ada 83 is *very* strict about enforcing the abstraction.  (i.e.:
private data types are *only* accesible through the defined interface.)
As a programmer who uses Ada 83 at work daily, this is both a blessing
and a curse.  But since I wrote the package, I can just add a necessary
function to the interface.  ;-)

I have also been reading about Ada 9X.  In the booklet "Introducing Ada
9X", Section 2.7, "Hierarchical Libraries", pp 20-23 and Section 2.8,
"Private Child Units", pp. 24-26 have text and code examples which
demonstrate these secion summaries (in the report's own words):

   The important special visibility rule is that the private part (if any)
   and the body of the child have visibility of the private part of their
   parent.

   The private part and body of any child can access the private part of
   its parent (and grandparent...).

Unless there is some subtlty that I've missed in the pages of *both* text
and code, all that one has to do to get access to the private datatypes
is to declare a child package.  (Note: this doesn't include renaming of
private interfaces, but does allow the foreign child to call private
interfaces and thereby effectively rename a private interface.)

Would an Ada programmer /ever/ knowingly defeat the intent of the package
interface and do this?  No, I don't think so.  Do you?  :-S

-- 
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