Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!cs.utexas.edu!pp!pink!rfg
From: rfg@pink.ACA.MCC.COM (Ron Guilmette)
Newsgroups: comp.lang.c++
Subject: Enums considered (ordered) integral?
Message-ID: <254@pink.ACA.MCC.COM>
Date: 19 Jun 89 16:18:31 GMT
Reply-To: rfg@MCC.COM (Ron Guilmette)
Organization: MCC  Austin, Texas
Lines: 52


Back in the bad old dayz, when we all used C and knew not of strict
typing rules, travesties like the following were perfectly legal
(and probably still are in ANSI C):

--------------------------------------------------------------------
enum color { red = 7, green = 11, blue = 9 };

color c;

int main ()
{
	for (c = 0; c <= blue; c++)
		continue;
}
---------------------------------------------------------------------

Interestingly, GNU G++ (1.35.0) eats this up without even a warning.
Could some kind soul tell me what Cfront 2.0 does with it?

I see *at least* three things which I consider errors here.

	1) The "c" variable is initialized (in the for loop) to a
	   non-color value.

	2) An (ordered) comparison operator is inappropriately used
	   to compare two values of a potentially *unordered* type
	   (i.e. the type "color").  Who sez that all enum types
	   represent types for which an ordering applies?  Ask
	   yourself "Is blue really greater than red?"

	3) The postfix operator ++ is applied to (what I consider to
	   be) a non-integral type variable.  This is the same issue
	   as (2) above, i.e. "Is there an ordering for colors?"
	   Another way of saying this is "Does it make any sense to
	   increment a color?"

All three of these (apparent) errors would still be errors even if
the declaration of color had been simply:

	enum color { red, green, blue };

The fact that my initial example included "representation specifications"
(to borrow an Ada term) for the values of type color, simply makes the
(apparent) errors more "glaring".


-- 
// Ron Guilmette  -  MCC  -  Experimental Systems Kit Project
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