Why doesn't strict complain here?

zentara has asked for the wisdom of the Perl Monks concerning the following question:

Hi, I just noticed an odd behavior in this Tk script, where a variable $b is used without being declared with "my $b", and strict dosn't issue a warning. Can someone tell me why?

#!/usr/bin/perl
use warnings;
use strict;
use Tk;
use Tk::Photo;
use Tk::JPEG;

# substitute any jpg file here, and it should be 
# scaled down by a factor of 4 and put in the 
# button
my $file   = "zen16.jpg";
my $w      = new MainWindow;

my $image1 = $w->Photo( -file => "$file", -format => 'jpeg' );

my $image  = $w->Photo();

$image->copy( $image1, -subsample => 4 );

$b = $w->Button( -image => $image )->pack();

$b->configure( -image => $image );

MainLoop;
[download]

I'm not really a human, but I play one on earth. Cogito ergo sum a bum

2006-07-05 Retitled by broquaint, as per Monastery guidelines
Original title: 'Why dosn't strict complain here'

Comment on Why doesn't strict complain here? Download Code

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Re: Why doesn't strict complain here by davorg (Chancellor) on Jul 05, 2006 at 12:45 UTC
`$a` and `$b` are special variables (because of their use in sort routines). They are therefore not subject to `strict` checks. -- <http://dave.org.uk> "The first rule of Perl club is you do not talk about Perl club." -- Chip Salzenberg	[reply]
Re: Why doesn't strict complain here? by derby (Abbot) on Jul 05, 2006 at 12:47 UTC
$a and $b are special vars (you really shouldn't use them). From perlvar: `Special package variables when using sort(), see "sort" in perlfunc. Because of this specialness $a and $b don't need to be declared (using use vars, or our()) even when using the "strict 'vars'" pragma. Don't lexicalize them with "my $a" or "my $b" if you want to be able to use them in the sort() comparison block or function.` [download] -derby	[reply] [d/l]
Re: Why doesn't strict complain here? by zentara (Cardinal) on Jul 05, 2006 at 12:51 UTC
Doh !!!! Thanks..... I need to post a dumb question once in awhile to keep up my reputation. :-) I'm not really a human, but I play one on earth. Cogito ergo sum a bum	[reply]
Re^2: Why doesn't strict complain here? by rodion (Chaplain) on Jul 05, 2006 at 17:52 UTC
Collision with "$a" and "$b" built-ins is one of the hazards of using single letter variables, along with making it difficult to search for the variable others maintaining code I used to think "$i" was just fine as an index variable, but my collegues, after grumbling in private for several years, convinced me that I could aford to type "$idx". (although it wasn't easy to give up the habit.)	[reply]
Re^3: Why doesn't strict complain here? by zentara (Cardinal) on Jul 06, 2006 at 13:27 UTC
Yeah, it's a bad habit from Engineering school where everything is x,y,z,w,t,i,j,k. I'm not really a human, but I play one on earth. Cogito ergo sum a bum	[reply]