Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!apple!usc!zaphod.mps.ohio-state.edu!uakari.primate.wisc.edu!aplcen!haven!mimsy!chris
From: chris@mimsy.umd.edu (Chris Torek)
Newsgroups: comp.lang.c
Subject: Re: C strongly typed?
Message-ID: <23014@mimsy.umd.edu>
Date: 10 Mar 90 05:51:40 GMT
References: <259@eiffel.UUCP> <1990Mar1.172526.28683@utzoo.uucp> <849@enea.se> <4440@ganymede.inmos.co.uk>
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 47

In some article somewhere someone claims that because

	f() {
		typedef int apple, orange;
		apple a;
		orange o = 1;

		a = o;
	}

compiles without complaint, C must therefore not be strongly typed.

>In article <2963@goanna.oz.au> ok@goanna.oz.au (Richard O'keefe) points out
that by this logic, neither is (part of) Ada:
>>	    subtype apple  is integer;
>>	    subtype orange is integer;

In article <4440@ganymede.inmos.co.uk> mph@lion.inmos.co.uk (Mike Harrison)
says to use instead
>	    type APPLE  is new INTEGER;
>	    type ORANGE is new INTEGER;

Well, if we are allowed to rewrite the code arbitrarily, I suggest

	typedef struct { int value; } apple;
	typedef struct { int value; } orange;

	f(void) {
		apple a;
		orange o = { 1 };	/* NB: requires ANSI C */

		a = o;
	}

which is (surprise surprise) illegal.

Those who will argue with Henry Spencer should read his original article
(and perhaps his followup; I cannot recall whether there was one) closely:
it says (paraphrased)

	a) typedef does not define a new type.
	b) `struct' defines a new type.
	c) If you want the compiler to complain, you must
	   therefore not rely on `typedef' alone.
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163)
Domain:	chris@cs.umd.edu	Path:	uunet!mimsy!chris