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Path: utzoo!utcsri!greg
From: greg@utcsri.UUCP (Gregory Smith)
Newsgroups: net.lang
Subject: Re: Multiple assignments
Message-ID: <2788@utcsri.UUCP>
Date: Sun, 18-May-86 13:23:42 EDT
Article-I.D.: utcsri.2788
Posted: Sun May 18 13:23:42 1986
Date-Received: Sun, 18-May-86 14:28:34 EDT
References: <1455@mmintl.UUCP> <825@bentley.UUCP>
Reply-To: greg@utcsri.UUCP (Gregory Smith)
Organization: CSRI, University of Toronto
Lines: 49
Summary: 

In article <825@bentley.UUCP> kwh@bentley.UUCP (KW Heuer) writes:
>In article <1455@mmintl.UUCP> franka@mmintl.UUCP (Frank Adams) writes:
>>... Supposing that "$" is being used for this ["multi-assignment"] operator,
>>then to set both "a" and "b" to zero, one would write "a $ b = 0", rather
>>than "a = b = 0", as C does....  
>
>>On the other hand, if your language supports argument passing by address,
>>it permits an output argument to be multiply assigned; something which
>>assignment-with-value does not support.
>
>What do you mean by this?  I don't see how this operator allows you to do
>anything that simple assignment doesn't.  Examples?

I think he means:
	procedure proc( var a : integer );
	begin
		a:= 0;
	end;
begin
	proc( cc $ dd );	{ set cc and dd to 0 }

I cannot agree with this - this is glorifying side-effects to a bizarre
extent. The implementation is not straightforward, either. Besides, what
if 'proc' looks at 'a' before using it?

>Btw (somebody is bound to point this out, may as well be me), the result of
>"a = b = x" in C is not really "b = x; a = x" as implicitly assumed above;
>it's "b = x; a = b".  (It makes a difference if a and b differ in width.)

Right. It's sometimes not better, either, if 'x' is easier to 'get' than
'b':
------- mung.c -----
main(){
	int a,b;
	a=0 ; b=0;
	a=b=0;
}
------  some of mung.a68 ----
	clrl	a6@(-4)		; a=0 (2 words )
	clrl	a6@(-8)		; b=0
	clrl	a6@(-8)		; b=0
	movl	a6@(-8),a6@(-4)	; a=b ( 3 words)

Of course, one can always say that the compiler should have fixed that :-).

-- 
"We demand rigidly defined areas of doubt and uncertainty!" - Vroomfondel
----------------------------------------------------------------------
Greg Smith     University of Toronto      UUCP: ..utzoo!utcsri!greg