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From: pem@frankland-river.aaii.oz.au (Paul E. Maisano)
Newsgroups: comp.lang.perl
Subject: Re: Creating a reference to an array index
Message-ID: <1362@frankland-river.aaii.oz.au>
Date: 18 Mar 90 02:50:45 GMT
References: <1361@frankland-river.aaii.oz.au> <1990Mar17.183039.21097@iwarp.intel.com>
Organization: Australian AI Institute
Lines: 50

In article <1990Mar17.183039.21097@iwarp.intel.com>, merlyn@iwarp.intel.com (Randal Schwartz) writes:
> 
> So I still don't know why you want to alias an element like that. :-(

This method probably does not buy you anything that you can't do with
associative arrays or using eval and coding things a little differently.

I can only give you the reason I was originally looking for a technique
like this. Say I have an array of buffers, @current_buffer indexed by
$current_line and I want to use it in a subroutine. I don't think it would
be uncommon to see something like the following at the start:
	sub handle_input {
	    local($buf) = $current_buffer[$current_line];
	    ...
From now on I can use $buf instead of the (more informative) but extremely
verbose $current_buffer[$current_line].

This is fine and good, everything works well. I have about 5 to 10
references to $buf in my subroutine which I think is easier to read than
the alternative. But as soon as realize that I need to start modifying
the buffer it stops working since $buf is only a copy. This is not
drastic. I can either go back to using the verbose form everywhere or
simply copy $buf back into the real buffer before every place I return
from the subroutine.

The problem seemed to me that I was using local in a different way than was
intended. I was trying to use it as an aliasing mechanism which it is not.
Now I can say
	local(*buf) = &ref($current_buffer[$current_line)];
to get the effect I was trying to achieve.

For anyone interested &ref can be defined as follows:
	sub ref {
		local($tmp);
		grep($tmp = *_, $_[0]);
		$tmp;
	}
This routine could be made more general by returning an array of
references for each argument. Ie. you could write,
	local(*x, *y, *z) = &ref($x[1], $y[0], $z[2]);

You could even set things up so that two arrays share elements!!
I'd better stop right here.. I feel a madness coming on :-)

------------------
Paul E. Maisano
Australian Artificial Intelligence Institute
1 Grattan St. Carlton, Vic. 3053, Australia
Ph: +613 663-7922  Fax: +613 663-7937
Email: pem@aaii.oz.au   UUCP: {uunet,mcsun,ukc,nttlab}!munnari!aaii.oz.au!pem