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From: throopw@xyzzy.UUCP (Wayne A. Throop)
Newsgroups: comp.lang.c
Subject: Re: interesting type problem
Message-ID: <279@xyzzy.UUCP>
Date: Mon, 28-Sep-87 14:19:18 EDT
Article-I.D.: xyzzy.279
Posted: Mon Sep 28 14:19:18 1987
Date-Received: Tue, 29-Sep-87 07:08:37 EDT
References: <8626@utzoo.UUCP>
Organization: Data General, RTP NC.
Lines: 36

> henry@utzoo.UUCP (Henry Spencer)
> Consider the following problem. [A type 'T' at least partially composed of
> a pointer to type 'T']  [...]
> It can't be done in strictly portable C using "efficient" pointers

True.  The problem is that C has no way to introduce a type by name
before or during the definition of that type, except with struct, union,
or enum.  Thus, there is no way to specify a recursive type, except inside
structures, unions, or enumerations.  I personally think that "typedef"
ought to do this, so that one could say things like

        typedef foo_t *foo_t;

to declare foo_t as a pointer type, pointing to foo_t.  Of course, this
complicates the parse of such things beyond belief (or it seems to... I
haven't really tried hard to come up with a simple scheme because it
looks so hopeless).  Perhaps a new keyword, such as "forward", which
could introduce a recursive typedef, so that something like:

        typedef forward foo_t;
        typedef foo_t *foo_t;

would work just fine, because foo_t can now be recognized as both a type
and the name being defined.  Though maybe even this doesn't solve it.

Sigh.

--
Inigo hated it there.  Everybody was so dangerous, big, mean and
muscular, and so what if he was the greatest fencer in the world, who'd
know it to look at him?  He looked like a skinny Spanish guy it might be
fun to rob.  You couldn't walk around with a sign saying "Be careful,
this is the greatest fencer since the death of the Wizard of Corsica. Do
not burgle."
                        --- From The Princess Bride by William Goldman
-- 
Wayne Throop      <the-known-world>!mcnc!rti!xyzzy!throopw