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From: jss@hector.UUCP (Jerry Schwarz)
Newsgroups: comp.lang.c++
Subject: Re: Use of inheritance for classification? (iostream)
Keywords: MI, iostream
Message-ID: <11563@ulysses.homer.nj.att.com>
Date: 20 May 89 16:52:37 GMT
References: <11557@ulysses.homer.nj.att.com> <30582@apple.Apple.COM> <10248@riks.csl.sony.JUNET> <329@odi.ODI.COM> <327@calmasd.Prime.COM> <3297@kalliope.rice.edu>
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Reply-To: jss@hector.UUCP (Jerry Schwarz)
Organization: AT&T Bell Laboratories
Lines: 40

I gave as an example:
    
    The iostream library that is scheduled to be part of 2.0 uses

    class ios { ... }
    
    class istream : virtual public ios { ... } ;
    
    class ostream : virtual public ios { ... } ;
    
    class iostream : public istream, public ostream { ... } ;
    
    Input operations are allowed on istreams.  Output operations on
    ostreams.  iostreams allow both operations (as when updating disk
    files)
    

In article <3297@kalliope.rice.edu> rich@kappa.Rice.EDU (Richard Murphey) 
presents a similar example

    
    class iostream : public istream, public ostream
    {
      iostream();
    };
    
    iostream::iostream() 
    :istream(stdin), ostream(stdout)
    { }


The idea of pairing an istream with an ostream in this way is
interesting, but it is subtly different from my example. The 2.0
iostream library puts the "data" into ios, so that an iostream has
only one set of data.   If Rich had done something that tried to
examine the error state (for example) he would have encountered
difficulties because there are two such in his iostream.

Jerry Schwarz
AT&T Bell Labs, Murray Hill