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From: bright@dataio.Data-IO.COM (Walter Bright)
Newsgroups: comp.lang.c
Subject: Re: swaps with arrays
Message-ID: <1361@dataio.Data-IO.COM>
Date: Thu, 10-Sep-87 14:25:44 EDT
Article-I.D.: dataio.1361
Posted: Thu Sep 10 14:25:44 1987
Date-Received: Sat, 12-Sep-87 09:46:36 EDT
References: <2376@zeus.TEK.COM> <110@umigw.MIAMI.EDU>
Reply-To: bright@dataio.UUCP (Walter Bright)
Organization: Data I/O Corporation; Redmond, WA
Lines: 48

In article <110@umigw.MIAMI.EDU> steve@umigw.UUCP (steve emmerson) writes:
>In article <1354@dataio.Data-IO.COM> bright@dataio.Data-IO.COM (Walter
>Bright) wrote:
>| Having a typeof would make creation of 'generic' routines possible:
>|	#define swap(a,b)	{ typeof(a) tmp; tmp = a; a = b; b = tmp; }
>
>To which I responded in article "<109@umigw.MIAMI.EDU> steve@umigw.UUCP"
>saying:
>+--------
>|[swap macro] also won't work with pure array objects (i.e. swapping one
>|array with another).  A generic routine should be able to work with
>|*anything*.
>+--------
>
>Well, I can't speak for everyone ;-), but if I was given a generic swap
>routine that only worked on a subset of all possible data types ...
>well, I might consider it very useful, but I wouldn't consider it
>generic.  Someone please correct me if I'm wrong, but I believe a
>"generic" routine is one that will work for any type of input (with a
>caveat for the above example that the two arguments have the same
>type).  Now, in the original article, Walter Bright had the word
>"generic" in quotes.  Perhaps he was thinking along these lines and
>ment to imply a "pseudo" or "quasi" generic routine (Walter?).

I did mean generic. I know that the above won't work with arrays. But
then, all battle-scarred C programmers know that how arrays work is
botched in C, they just don't work like other types:

	int a[5],b[5];

	a = b;			/* copy contents of b to a	*/
	if (a == b)		/* if contents match		*/
		...
	func(a);		/* push entire array on stack	*/

Of course, none of the above works as 'expected'. This also means that
the usefulness of typedef's is compromised, you still have to be
cognizant if your typedef is an array or a struct or a basic type.

The symmetry and beauty of a language is inversely proportional to the
number of
	if (special case)
		then kludge;
constructs in the parser. A quick look at my compiler (Datalight) sources
confirms that C is jammed with ifs!

Don't get me wrong, C is my language of choice for most of my programs.
But it does have its flaws...