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From: kwh@bentley.UUCP (KW Heuer)
Newsgroups: net.lang.c
Subject: Re:  A good use of a bad feature
Message-ID: <800@bentley.UUCP>
Date: Fri, 9-May-86 00:18:07 EDT
Article-I.D.: bentley.800
Posted: Fri May  9 00:18:07 1986
Date-Received: Sat, 10-May-86 07:54:22 EDT
References: <528@brl-smoke.ARPA>
Organization: AT&T Bell Laboratories, Liberty Corner
Lines: 37
Summary: Fall-thru is *not* better!

In article <528@brl-smoke.ARPA> root@icst-cmr ((Root Boy) Jim Cottrell) writes:
[concerning the fall-through case feature]
>You will find much disagreement on that point, I'm afraid. Fall thru is
>more flexible. You can always break, but often cases are related so that
>a particular case requires a superset of another case. It is to DMR's
>credit that he realized this feature. I sure wouldn't have thought of it.

An alternate implementation would have been for cases to be distinct by
default, but "continue" at the bottom of a case would cause a fall-thru.
(In this model, "break" would be meaningless inside a switch and "continue"
would be meaningful, instead of the opposite.)  Given that most use of the
switch statement *does* have distinct cases, and the exceptions are often
explicitly labeled /* no break */, I think this would've been better.
(I would *almost* accept a model with automatic break and no keyword for
fall-thru, and suffer the occasional goto.)

One special instance is where the superset is actually an equivalence, i.e.
two or more labels on the same code:
	case ' ':
	case '\t':
	case '\n':
		white();
		break;
This would be ugly with the auto-break model, but the solution is to allow
	case ' ','\t','\n':
		white();
which I think looks neater anyway.

(Btw, I find
	case '0':
	...
	case '9':
		digit();
annoyingly verbose in the current model, and often use "if" rather than
"switch" because of it.)

Karl W. Z. Heuer (ihnp4!bentley!kwh), The Walking Lint