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From: rcd@opus.UUCP (Dick Dunn)
Newsgroups: net.lang.c
Subject: casts and puns (and digressions...)
Message-ID: <940@opus.UUCP>
Date: Wed, 7-Nov-84 05:39:39 EST
Article-I.D.: opus.940
Posted: Wed Nov  7 05:39:39 1984
Date-Received: Thu, 8-Nov-84 20:07:04 EST
References: <110@ISM780B.UUCP>
Organization: NBI,Inc, Boulder CO
Lines: 30

> ...  Do not be misled by the fact that some casts on some machines
> generate no code.  A cast is a *conversion*, not a type pun...

Unfortunately, not entirely true.  What C calls "casts" covers both
true casts (in, say, the ALGOL 68 sense) and puns, at least in practice.
The operation is a cast when conversion "makes sense" (in semantic terms);
otherwise it's a pun.  For example, if i is an integer, (float)i is clearly
a cast; it generates instructions on most machines and produces a different
internal datum which is the float corresponding most closely to the
integral value of i.  However, (long*)i is a pun; you just have to stretch
too far to make any sensible semantics which makes it a true cast.

> >example 'struct foo {struct foo *ref;};'...
> struct foo is not a recursive type.  At best you might call it an
> iterative type.  What would you think of struct foo {struct foo bar;}; ?

Please be careful when attacking other folks' terminology.  Structured
types which contain references to themselves are quite commonly called
"recursive".  (See, for example, Hoare's seminal paper "Notes on Data
Structuring".)

> >Also, Pascal, which is doubtlessly a strongly typed language, does
> >permit a type definition like 'type ref= ^ref;' and handles it
> >correctly...

Perhaps true, but marginally relevant to reality, since the only value
assignable to an object of type ref is NIL.
-- 
Dick Dunn	{hao,ucbvax,allegra}!nbires!rcd		(303)444-5710 x3086
   ...Never attribute to malice what can be adequately explained by stupidity.