Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!ncar!tank!shamash!nic.MR.NET!thor.acc.stolaf.edu!mike
From: mike@thor.acc.stolaf.edu (Mike Haertel)
Newsgroups: comp.lang.c++
Subject: Re: the secret bang
Message-ID: <7385@thor.acc.stolaf.edu>
Date: 17 Oct 89 04:09:59 GMT
References: <1167@osc.COM>
Reply-To: mike@thor.stolaf.edu ()
Organization: St. Olaf College, Northfield, MN
Lines: 31

In article <1167@osc.COM> strick@osc.com (henry strickland 415-325-2300) writes:
>// Here's one for your C++ puzzle book.
> [ . . . ]
>// Curious to AT&T cfront2.0 is the undocumented postfix-bang operator.
>// It can only be used in type declarations, to mean the same thing as
>// the prefix-star operator or the postfix-empty-brackets operator.
>// The secret bang is demonstrated in v4(), v5(), and r4().
> [ . . . ]
>// Any conjectures why the secret bang is there?  Wasn't postfix "!" a
>// dereference operator in BCPL?  Know of any other C or C++
>// implementations that accept it?

Obviously, the use of a postfix "pointer" declarator obviates
the need for the (sometimes very tricky) parenthesization
of complex declarations.

Consider the (C) declaration:

	void (*signal(int, void (*)(int)))(int);

If we take ! as a postfix declarator that means the same as *
we get:

	void signal(int, void !(int))!(int);

which can literally be read from left to right.  Ravi Sethi
wrote a really neat paper about this.
-- 
Mike Haertel <mike@stolaf.edu>
``There's nothing remarkable about it.  All one has to do is hit the right
  keys at the right time and the instrument plays itself.'' -- J. S. Bach