Path: utzoo!attcan!uunet!lll-winken!lll-lcc!ames!husc6!wjh12!redsox!campbell
From: campbell@redsox.UUCP (Larry Campbell)
Newsgroups: comp.lang.c++
Subject: Improved switch statement (was Re: goodbye cpp ???)
Message-ID: <574@redsox.UUCP>
Date: 16 Dec 88 03:26:39 GMT
References: <6590072@hplsla.HP.COM> <1106@etive.ed.ac.uk> <33528@bbn.COM> <1907@ogccse.ogc.edu>
Reply-To: campbell@redsox.UUCP (Larry Campbell)
Organization: The Boston Software Works, Inc.
Lines: 49

In article <1907@ogccse.ogc.edu> wm@ogccse.UUCP (Wm Leler) writes:
}I don't think you could extend switch statements to work on strings,
}since there is some ambiguity between whether you want to compare
}the strings by comparing their contents (using strcmp) or by comparing
}their pointers (a very reasonable thing to do).

You leave that decision to the person who implemented == for the class.
I think it would be eminently sensible for the switch statement to operate
on any type that has an == operator defined; of course the case labels would
have to be the correct type (or coerced thereto).

A common and useful idiom I learned in BLISS which is, unfortunately, not
possible in C or C++ today, is the following code fragment (transliterated
from BLISS into pseudo-C), which checks a number of boolean flags:

	bool flag1, flag2, flag3;
	switch (TRUE)
	    {
	    case flag1:
		// stuff
	    case flag2:
		// stuff
	    case flag3:
		// stuff
	    default:
		// whatever
	    }

I think this is much clearer and neater and far less prone to error during
maintenance than the current alternative:

	bool flag1, flag2, flag3;
	if (flag1)
	then
	    // stuff
	else
	    if (flag2)
	    then
		// stuff
	    else
		if (flag3)
		then
		    // stuff
		else
		    // whatever

-- 
Larry Campbell                          The Boston Software Works, Inc.
campbell@bsw.com                        120 Fulton Street
wjh12!redsox!campbell                   Boston, MA 02146