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From: jbuck@galileo.berkeley.edu (Joe Buck)
Newsgroups: comp.lang.c++
Subject: Re: asking an object for its type
Message-ID: <11284@pasteur.Berkeley.EDU>
Date: 20 Feb 91 01:37:54 GMT
References: <23984@netcom.COM> <1190@sheol.UUCP> <1991Feb19.000449.22255@gpu.utcs.utoronto.ca> <607@taumet.com> <65451@brunix.UUCP>
Sender: news@pasteur.Berkeley.EDU
Reply-To: jbuck@galileo.berkeley.edu (Joe Buck)
Lines: 33

In article <65451@brunix.UUCP>, sdm@cs.brown.edu (Scott Meyers) writes:
|> The bottom line is that virtual functions are wonderful things and can
|> almost always be used to achieve what you want, but there are times when
|> you truly *do* need to get type information as you run.

Scott then goes on to talk about how the ANSI committee is unlikely
to give him what he wants.

What do you care what the committee says?  If you must have this feature,
write, in the baseclass

	virtual const char* myType() = 0;

then do

const char* ControlArc::myType() { return "ControlArc";}

It is already in the language if you must have it.  However, I would still
discourage you from this type of programming.

Why?  Because people will add new types of Arcs and you won't deal with
them properly.  You're dealing with objects based on an exact match of
some type string instead of based on some relevant attribute that a
virtual function could return.  You're wiring in a list of classes you
can handle, requiring more code rewriting as classes are added.

But if you really want to do it, you can, so stop saying that C++ won't
give you run-time type information.  It's trivial to add if you want it.


--
Joe Buck
jbuck@galileo.berkeley.edu	 {uunet,ucbvax}!galileo.berkeley.edu!jbuck