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From: dewar@merv.cs.nyu.edu (Robert Dewar)
Subject: Re: packages and private parts
Date: 1997/02/07
Message-ID: <dewar.855349349@merv>#1/1
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references: <32F170C8.6A88F208@cam.org> <dewar.854838063@merv>
 <32FA4C67.48D9@watson.ibm.com> <dewar.855276290@merv>
 <32FB51D8.1C90@watson.ibm.com>
organization: New York University
newsgroups: comp.lang.ada
Date: 1997-02-07T00:00:00+00:00
List-Id: <comp.lang.ada>


<<Robert is right that I was unable to persuade enough people (i.e., a set
of people that included Tucker Taft :-) ) of this position, although
concern about this issue was widespread.  My ally in this argument,
David Pogge, was unable to carry the day even with his colorful warnings
about the "Howard Hughes effect"--total strangers declaring themselves
to be your children.  Indeed, Tucker eventually won me over me with his
argument that adding a child to a package should be viewed as the moral
equivalent of modifying the text of the package.
>>

I know there is a smiley there, but still, I think this should not go
unanswered. My memory was that VERY few people were convinced, I certainly
was not, I thought the suggestion of absolute privacy was a serious mistake,
and i still do, and that is the same view that a majority of people had!

<<Long after consensus had been achieved that child packages, with their
associated visibility rules, would be a part of Ada 95, I realized that
a far more serious concern than the Howard Hughes effect was the way in
which child visibility into private declarations of the parent muddied
the contractual interface of a library package, restricting the freedom
of the package's author to change the implementation of a private type
in a later version of a fielded package.  (I discussed this concern in
more detail in another post yesterday.)  I wish this argument had
occurred to me earlier.
>>

Well that argument was made clearly, if not by you, then by others, and
was still not convincing.

I repeat my earlier suggestion. I think this concern is a straw man. I
certainly have not seen any problems arising in real application programs
from this concern, has anyone else? I am not talking about cases you
can construct in your mind, I am talking about real cases from real
applications!

Certainly it would be perectly fine to add a pragma restricting visibility
in the manner Norman suggests, but this issue has never come up among the
thousands of people actually using Ada 95, so it seems to me this is a
case where the majority and Tuck and the RM all agree, and it's a good
thing that they do!