Re: detecting changes in a localised variable

Here I tie $_ to a Complainer package that can warn/carp/croak any time something tries to assign to it.

#!perl -l

package Complainer;
use Tie::Scalar;
use base Tie::StdScalar;
use Carp;

sub STORE {
   # Warn out any status info you want here.
   carp "Tried to assign to \$_";
}

sub FETCH { $_ }

package main;

tie $_, Complainer;

$_ = 1;

local $_;
[download]

Update: Added the fetch method so that reading $_ actually works. not sure why I have to do that, Tie::StdScalar should handle that for me... but this was written in a hurry.

Ted Young

($$<<$$=>$$<=>$$<=$$>>$$) always returns 1. :-)

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Re^2: detecting changes in a localised variable by Tanktalus (Canon) on Feb 18, 2005 at 22:46 UTC
Tie? That's an idea I obviously didn't have. However, when trying your code, which I am ever so grateful for, I noticed that local $_ caused the carping - which was what I was trying to avoid. Since $_ was now localised, I didn't care if it was being changed because that's kinda like a new value. Somewhere in my do_something_complex function, I'm causing a file to be loaded (only once - there's lots of caching going on). And that file load has a "`while (<$fh>)`" line in it to parse out the file. And so I'm getting about a bazillion carps - even after localisation. Hopefully this helps make my original query more clear... maybe not possible, but clear :-) Update: That all said, this file load was the problem. So my code is cleaner now because of this, although the general question is, I think, a useful question - how to determine a variable changing, discounting any localised changes. In other words, a variable whose change will propogate back up the call stack.	[reply] [d/l]
Re^3: detecting changes in a localised variable by TedYoung (Deacon) on Feb 18, 2005 at 23:15 UTC
Yes, I was about to mention, as I was reading your post: `while (<FH>) {` [download] does not localize $_ Ted Young `($$<<$$=>$$<=>$$<=$$>>$$) always returns 1. :-)`	[reply] [d/l] [select]