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From: dale@cs.rmit.edu.au (Dale Stanbrough)
Subject: Re: Private Children
Date: 1999/06/24
Message-ID: <dale-2406990948380001@dale.cs.rmit.edu.au>#1/1
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Organization: RMIT
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Newsgroups: comp.lang.ada
Date: 1999-06-23T23:48:37+00:00
List-Id: <comp.lang.ada>

Richard D Riehle wrote:

  An opaque type is a type that contains nothing but a reference to
  data. This is quite easy using Ada's incomplete type definition.
  These can be tagged for extensibility while hiding all the details
  within a package body.  Consider..."

Yes, but that forces me to change the representation that I may have
chosen for very good reasons, just to get around what I view is a 
problem in how "private" works for packages.


" In the final analysis, though, encapsulation is something like the
  lock on a safe that is intended to keep honest people honest. If 
  someone is determined to break encapsulation, they will find a way
  to do it, even if they have to crack open your package body and
  perform "open heart surgery.""


Yes, but this doesn't really address the issue at hand. What I am
arguing is that Ada could have been -more- helpful than it is in
supporting encapsulation, not that we need not worry about it encapsulation
because people can break it if they want to (after
all anyone can use unchecked-perversion to open up any private type
they like!).

Certainly encapsulation doesn't (or rather in Ada's case, shouldn't)
end at the level of package hierachies.


Dale