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From: roman@sparc7.hri.com (Roman)
Newsgroups: comp.lang.c++
Subject: Re: Filesystem classes: how to?
Message-ID: <1990Jun7.214800.14989@hri.com>
Date: 7 Jun 90 21:48:00 GMT
References: <1567@swbatl.sbc.com>
Sender: news@hri.com
Reply-To: roman@sparc7.hri.com (Roman)
Organization: Horizon Research
Lines: 40

In article <1567@swbatl.sbc.com>, gilstrap@swbatl.sbc.com (3929) writes:
> Okay, anyone want to give a stab at a set of classes to implement a Unix file
> system?  My initial thoughts were:
> 
>                               FileSystemNode
>                                    |
>                +------------+--------------+-------+---------+
>                |            |              |       |         |
>            Directory  CharacterFile   BlockFile  Link  SymbolicLink
>                             |
>                   +-------------------+
>              RegularFile     CharacterSpecialFile
> 
[deleted]
> Anyone have any suggestions?
> 
> Brian R. Gilstrap
> uucibg@swbatl.uucp OR ...!{ texbell, uunet }!swbatl!uucibg
>
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~
> "You spend your whole life just piling it up there.  You got stacks
and stacks
> and stacks.  Then Gabriel comes and taps you on the shoulder, but you
don't see
> no hearses with luggage racks."
>                              --- Don Henley
>
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~
> Copyright (c) 1990 by Brian R. Gilstrap.  You may redistribute (my
portions of)
> this material for free if and only if your recipients may also do so.

You have to design everything into FileSystemNode, that is create
virtuals for all possible subclasses, so you can access them through the
base pointer. You also have to somehow know the type in run time ( or
have the base class virtuals respond appropriately).
Not very pretty, but the only way I found. I guess it's OK when you
design the whole system. Hard to extend tho.