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From: lpringle@bbn.com (Lewis G. Pringle)
Newsgroups: comp.lang.c++
Subject: Re: goodbye cpp ???
Message-ID: <33528@bbn.COM>
Date: 14 Dec 88 18:27:34 GMT
References: <6590072@hplsla.HP.COM> <1106@etive.ed.ac.uk>
Sender: news@bbn.COM
Reply-To: lpringle@labs-n.bbn.com (Lewis G. Pringle)
Organization: Bolt Beranek and Newman Inc., Cambridge MA
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>The current definition of C++ can't do half the things that the CPP can.
>For example, inline functions can't replace macros that have declarations
>or constant expressions on their rhs.  An example of the latter is:
>
>#define CTRL(x)  (x - 0100)
>...
>   case CTRL('A'):
>
>Not that I'd mind a bit more restriction on what the preprocessor could
>do -- just as long as I can still do all the things *I* want (semi ;-).

This example reminds me of a suggestion for an extention to C++.  The problem
with the above code is that switch statements require the cases to be integer
constants - though there is really no good reason for this.

All too often I have seen code like
	if (a == thing1) {
	}
	else if (a == thing2) {
	}
	...
where either a is not an inteer, or the things are not constant.  Sometimes
the == is replaced by a strcmp().

When c++ sees a switch statement, it could generate the skip-chain
of if-then-elseifs from that, so long as the argument to the switch
and the cases where all =='able.  (As an optimization - of course -
when the cases are all constant it could just output the C switch statement
as-is.)

For example, the cfront could translate
	switch (GetSomeStringFromSomeWhere) {
		case "Fred": {
		}
		break;
		case "Barny": {
		}
		break;
	}
into the obvious if-then-else chain.

NB: This example assumes an class String() with op== and String(char *)

I guess there is one implicit assumtion in all of this, and that is
that the case statement is clearer than the long list of if-then-elses,
but I take that for granted.  I also realize that this might be taken
as a bit kitchen-sinky.  Still, I think that it would make C++ an
even-better C :-).

					Lewis.



"OS/2: half an operating system for half a computer."

In Real Life:		Lewis Gordon Pringle Jr.
Electronic Mail:	lpringle@labs-n.bbn.com
Phone:			(617) 873-4433