Path: utzoo!utgpu!water!watmath!clyde!cbosgd!ihnp4!homxb!whuts!mtune!rutgers!rochester!ritcv!cci632!ccicpg!nick
From: nick@ccicpg.UUCP (Nick Crossley)
Newsgroups: comp.lang.c
Subject: Re: == vs =
Summary: Other assignment operators
Keywords: C,assignment,displacement
Message-ID: <9998@ccicpg.UUCP>
Date: 26 Jan 88 20:14:44 GMT
References: <626@PT.CS.CMU.EDU> <214@oink.UUCP> <2681@mmintl.UUCP>
Reply-To: nick@ccicpg.UUCP (Nick Crossley)
Organization: CCI CPG, Irvine CA
Lines: 16

While we are inventing other types of and syntax for assignment,
what about the 'displacement' operator which we had in the Algol68C
compiler designed by (amongst others) SR Bourne (before he went to
Bell to write sh)?

This was written ':=:=', and had the same effect as ':=' in that it
assigned the value on the right to the variable on the left (loose
terminology, I know), but the value of the whole expression was the
OLD value of the left hand side, rather than the NEW value as with ':='.

This was useful in MANY constructs.  One (not very frequent) example
is that of swapping two values :-

	a := b :=:= a;

The operate-and-displacement forms were also provided (+:=:=, -:=:=, etc.)