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From: rcd@nbires.UUCP
Newsgroups: net.lang.c
Subject: Re: WITH statement
Message-ID: <470@opus.nbires.UUCP>
Date: Mon, 21-Jul-86 02:25:09 EDT
Article-I.D.: opus.470
Posted: Mon Jul 21 02:25:09 1986
Date-Received: Mon, 21-Jul-86 07:37:24 EDT
Organization: NBI,Inc, Boulder CO
Lines: 50
Summary: no danger--it's like a procedure

> The ambiguous condition scares me too, and I think I could live
> much better with being able to take the address of the thing
> and then using it, like:
> 
>        recpointer := &recarray[selector];
>        ...
>        recpointer^.foo := 1;
>        recpointer^.bar := 2;

I don't intend to flame, but there's a funny ring to this sort of view of
the (Pascal) `with' statement.  C programmers roundly criticize Pascal as
being more cumbersome in notation.  I generally agree; Pascal could allow
more terse expression without suffering...but then why is it scary when
Pascal has a construct which allows more terse expression than C?

First off, the standard disclaimer:  the `with' statement can be abused, as
can any statement (including the null statement!) in any language.

The `with' statement is an interesting construct from a programming
language standpoint; I don't know of too many others in its class.  One way
to think of it is as a procedure:
	with p^, q[i] do...
is like starting a procedure right there with (value) parameters being the
records given.  Within the procedure you have access to these objects which
is more convenient and presumably more efficient.  It's a funny open-code
sort of thing.

Opening a with using two records of the same type is possible, but rare
because it's kind of silly.  (It has nowhere near the potential for screwup
of, say, calling a procedure with two pointer parameters pointing to the
same object.)

The "scary" part of the `with' statement--the loss of qualifier in front of
field selectors--is no problem at all in practice because `with' statements
tend to be intensive activity on the records being manipulated.  I've
observed that `with' statements tend to be either fairly short (probably
under 10 lines) or the entirety of a procedure where the `with' opens one
or more of the procedure's parameters--for example:
	procedure xxx(p: pwhatzy);
	...decls
	begin with p^ do begin
	...work on the object referenced by p
	end end;

I've written a lot of Pascal and a lot more C.  Mostly I find C faster to
write, but when I start writing a sequence of code to fill in a structure,
I sure miss the `with' statement.
-- 
Dick Dunn	{hao,ucbvax,allegra}!nbires!rcd		(303)444-5710 x3086
   ...At last it's the real thing...or close enough to pretend.