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,c7d1d12d1859ad7f
X-Google-Attributes: gid103376,public
X-Google-ArrivalTime: 1995-02-08 21:55:21 PST
Path: 
 nntp.gmd.de!newsserver.jvnc.net!nntpserver.pppl.gov!princeton!udel!gatech!howland.reston.ans.net!news.sprintlink.net!solar.sky.net!solar.sky.net!jhoward
From: jhoward@solar.sky.net (John Howard)
Newsgroups: comp.lang.ada
Subject: Re: An Ada9X mimic of C++ friends?
Date: 9 Feb 1995 05:55:21 GMT
Organization: SkyNET Corporation
Message-ID: <3hcao9$96b@solar.sky.net>
References: <3h7u4p$8cp@bellboy.ucc.uconn.edu> <3hareb$nq5@lang8.cs.nyu.edu>
NNTP-Posting-Host: solar.sky.net
X-Newsreader: TIN [version 1.2 PL2]
Date: 1995-02-09T05:55:21+00:00
List-Id: <comp.lang.ada>

Cyrille Comar (comar@cs.nyu.edu) wrote:
: needham@newsserver.uconn.edu (Donald M Needham) writes:
: : Is there a construct in Ada9x that circumvents data abstraction
: : similar to a friend in C++?

: You can use the private part of a child unit (or a private child) to
: more or less simulate C++ friends. I say "more or less" because the
: "privacy" in C++ is an attribute of the Class where it is an attribute
: of the package in Ada and Ada package ARE NOT to be compared to C++
: Classes. The right equivalent to C++ classes in Ada95 are private or
: record types (depending on what level of data abstraction you
: want). Those types being "tagged" if you expect to need run-time
: dispatching or type extension.

: Cyrille Comar,                                  E-mail: comar@cs.nyu.edu
: Gnat Project                                    US phone: (212) 998-3489

I come from a background with Borland Pascal dialects and recently I was 
investigating Extended Pascal (ISO 10206:1991) and the latest 
"Object-Oriented Extensions to Pascal" (ANS TR13 or X3J9/93-033).  With 
Borland Pascal and C++ it was required to indicate in the definition of a 
method whether it could be overridden (e.g. virtual) in a descendant class.

Extended Pascal takes the opposite approach.  According to Appendix D.12 
in X3J9/93-033 "Any visible method can be overridden in a descendant class.
A requirement to specify that a method can be overridden thwarts 
specialization and code refinement.  It also requires an omniscient 
designer who anticipates future use; or, it requires the user must have 
access to the underlying code so that it can be changed.  Both of these 
are poor assumptions."

I am new to Ada.
So my question is: does the explicit use of "TAGGED" in Ada95 have the same 
negative consequences as specifying "virtual"?