Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.milw.wisc.edu!cs.utexas.edu!uunet!cimshop!davidm
From: davidm@cimshop.UUCP (David Masterson)
Newsgroups: comp.lang.c++
Subject: Re: Objectifying incoming messages?
Message-ID: <448@cimshop.UUCP>
Date: 29 Jul 89 01:22:09 GMT
References: <444@cimshop.UUCP> <1273@cbnewsl.ATT.COM>
Organization: Consilium Mt. View CA
Lines: 27
In-reply-to: dog@cbnewsl.ATT.COM's message of 27 Jul 89 13:57:45 GMT

>The same problem arises reading objects from disk.  Until you look at
>the data, you don't know what class of object to instance so it
>can read itself.  It seems to me, this is one place you still
>need a header/type field and a switch statement.
>
Agreed.  In fact, my messages deal with a database server to get information
from the database.  I think a function pointer table is a cleaner way of
implementing this in C, but can you implement an object construction pointer
table in C++?  By the way, would the object/function that reads from the
external entity be a separate thing or should it be a base class that looks at
itself and casts to the appropriate derived class (can that even be done?!?)?
Consider:

1.  All external objects have a common header in order to determine what type
of object they are.

2.  A generic object would get the external object and decide what to do with
it.

3.  Once it decides, it makes (casts) itself a specific object of the
appropriate type.

What problems are there in this method?  I think I see a few, but I'm curious
about what others think?  (I'm looking for ammunition ;-)

David Masterson
uunet!cimshop!davidm