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: 103376,23cf9f1e93744eed X-Google-Attributes: gid103376,public X-Google-ArrivalTime: 2003-07-30 22:57:25 PST Path: archiver1.google.com!news1.google.com!newsfeed.stanford.edu!headwall.stanford.edu!newshub.sdsu.edu!elnk-nf2-pas!newsfeed.earthlink.net!stamper.news.pas.earthlink.net!newsread4.news.pas.earthlink.net.POSTED!not-for-mail From: "Matthew Heaney" Newsgroups: comp.lang.ada References: <3F228F3B.9020203@attbi.com> <3F22F9E9.3040307@attbi.com> <5jn9ivoetll1fu2avn9hmjj6aaa7q7pmjn@4ax.com> Subject: Re: Need advice re package organization. X-Priority: 3 X-MSMail-Priority: Normal X-Newsreader: Microsoft Outlook Express 6.00.2800.1158 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1165 Message-ID: <9d2Wa.301$jp.253@newsread4.news.pas.earthlink.net> Date: Thu, 31 Jul 2003 05:57:25 GMT NNTP-Posting-Host: 65.110.133.134 X-Complaints-To: abuse@earthlink.net X-Trace: newsread4.news.pas.earthlink.net 1059631045 65.110.133.134 (Wed, 30 Jul 2003 22:57:25 PDT) NNTP-Posting-Date: Wed, 30 Jul 2003 22:57:25 PDT Organization: EarthLink Inc. -- http://www.EarthLink.net Xref: archiver1.google.com comp.lang.ada:41057 Date: 2003-07-31T05:57:25+00:00 List-Id: "Warren W. Gay VE3WWG" wrote in message news:clWVa.4191$mv6.741217@news20.bellglobal.com... > > The problem occurs in the private child package (IMO) because > you want to derive new objects from parent tagged records. The > danger that develops is that the child package's body code may > monkey with things in the parent object that you don't want it > to (this is lack of information hiding). That the private part of the parent package is visible to (the private part of) a child is a feature of the language. Yes, there is a "lack of information hiding," but the syntax of the language is designed so that it's obvious who has access to the private information, e.g. if I see P.C, I know that C has visibility to P. This is a consequence of the fact that visibility in Ada is controlled by the module relationship. One issue in C++ is that if I have: class B { public: virtual ~B(); protected: secret_t m_secret; }; then yes, this says that data member m_secret is visible to classes that derive from B, but there's nothing that identifies which classes those are. If I see a class D, there's nothing to tell me that D derives from B (unless you look at D's declaration, of course). This is why I usually name derived classes by tacking the derived name onto the base class name, e,g class Presentation { /* ... */ }; class PresentationAVI : public Presentation { /* ... */ }; etc class Stream { /* ... */ }; class StreamAVI : public Stream { /* ... */ }; class StreamWAV : public Stream { /* ... */ }; etc. At least in Ada, if I have one type that derives from another, e.g. package P is type T is tagged ...; ... end P; package P.C is type NT is new T with ...; ... end P.C; then at least when I see P.C.NT, I know immediately that C can see the private part of P. So I don't agree that one should that a parent package should try to "hide" stuff from a child. The set of modules that have visibility to the private part of P (and hence, that need to be consulted if there is a change) is bounded, and clearly demarcated. In the typical case the members of a package hierarchy (the "subsystem") would be kept together in a project, probably in the same directory, and maintained by a single person.