Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!purdue!decwrl!decvax!ima!haddock!karl
From: karl@haddock.ima.isc.com (Karl Heuer)
Newsgroups: comp.std.c
Subject: Re: Multiple typedefs
Keywords: typedefs, includes, defines
Message-ID: <12955@haddock.ima.isc.com>
Date: 3 May 89 22:09:19 GMT
References: <2322@lethe.UUCP> <10167@smoke.BRL.MIL> <2402@lethe.UUCP> <10190@smoke.BRL.MIL>
Reply-To: karl@haddock.ima.isc.com (Karl Heuer)
Organization: Interactive Systems, Boston
Lines: 22

In article <10190@smoke.BRL.MIL> gwyn@brl.arpa (Doug Gwyn) writes:
>In article <2402@lethe.UUCP> dave@lethe.UUCP (Dave Collier-Brown) writes:
>>[why are repeated typedefs illegal?]
>
>Well, consider how the compiler is going to parse a complex declaration
>containing several typedefs.  How does it know whether you are defining the
>same typedef a second time or are just using it to help typedef something
>else?

It seems to me that the compiler is going to have to be able to handle such a
case anyway.  Note that
	typedef int foo;
	void f(void) {
	    typedef int foo;
	}
*is* legal (and would be even if the two types didn't match; the second simply
hides the first until end-of-scope).  At the point of the second declaration,
the compiler has to be prepared for both a redeclaration of foo and a new
declaration using foo.  Given a compiler that can parse this, it would seem
that the extra effort to handle the desired feature would be negligible.

Karl W. Z. Heuer (ima!haddock!karl or karl@haddock.isc.com), The Walking Lint