Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.1 6/24/83; site decvax.UUCP
Path: utzoo!linus!decvax!minow
From: minow@decvax.UUCP (Martin Minow)
Newsgroups: net.lang.c
Subject: Array by value
Message-ID: <171@decvax.UUCP>
Date: Thu, 18-Aug-83 18:39:51 EDT
Article-I.D.: decvax.171
Posted: Thu Aug 18 18:39:51 1983
Date-Received: Fri, 19-Aug-83 01:40:25 EDT
Organization: DEC UNIX Engineering Group, Merrimack, NH
Lines: 38

Arnold Robbins suggests adding the ` operator to C to mean
"array by value" as in:

    int a[10]; b[10];
    ...
	`a = `b;	/* I may have misrembmered the syntax */

There are several problems with this.  First, all C expressions
return a value, so I should be able to write statements such
as

	if ((`a = `b) != 0)

which is going to cause great pains for compiler writers.

The other problem is that this suggestion rejects one of the
primary C design philosophies -- that of making "easy things
easy and hard things hard".  Most compiler writers will
generate something like "`a = `b":

	_bcopy(&a[0], &b[0], sizeof a);

A suitably written _bcopy will run at memory speeds for all non-trivial
cases.

I am willing to bet that all the reasonable "array by value"
operations could be implemented just as efficiently by
a macro preprocessor.

I should also note that Andrew's other suggested operator, '$'
is valid in identifiers in Vax-11C, Decus C, and probably
a few other PDP-11 compilers running on Dec machines.  ('$' is
necessary to access system-wide variables on Dec operating
systems.)

Martin Minow
decvax!minow