Comments on: Interesting Perl Behavior http://www.dangoldin.com/2008/05/30/interesting-perl-behavior/ My thoughts and musings Mon, 10 Jan 2011 08:03:00 +0000 hourly 1 http://wordpress.org/?v=3.3.1 By: Mark Tiefenbruck http://www.dangoldin.com/2008/05/30/interesting-perl-behavior/comment-page-1/#comment-5 Mark Tiefenbruck Tue, 05 Aug 2008 21:24:09 +0000 http://www.dangoldin.com/blog/?p=17#comment-5 They're not global. They're still limited in scope. The value just doesn't get reset when the same scope is entered more than once. Although known for years, it's been kept because, instead of reporting it as a bug, people started using this to implement static variables. It certainly wasn't smart, but that's what happened, and now we're stuck with it. Perl 6 will probably fix it. They’re not global. They’re still limited in scope. The value just doesn’t get reset when the same scope is entered more than once. Although known for years, it’s been kept because, instead of reporting it as a bug, people started using this to implement static variables. It certainly wasn’t smart, but that’s what happened, and now we’re stuck with it. Perl 6 will probably fix it.

]]> By: Zbigniew Lukasiak http://www.dangoldin.com/2008/05/30/interesting-perl-behavior/comment-page-1/#comment-4 Zbigniew Lukasiak Tue, 05 Aug 2008 18:20:06 +0000 http://www.dangoldin.com/blog/?p=17#comment-4 <blockquote>NOTE: The behaviour of a my statement modified with a statement modifier conditional or loop construct (e.g. my $x if ... ) is undefined. The value of the my variable may be undef, any previously assigned value, or possibly anything else. Don't rely on it. Future versions of perl might do something different from the version of perl you try it out on. Here be dragons. </blockquote> from http://perldoc.perl.org/perlsyn.html Cheers, Z.

NOTE: The behaviour of a my statement modified with a statement modifier conditional or loop construct (e.g. my $x if … ) is undefined. The value of the my variable may be undef, any previously assigned value, or possibly anything else. Don’t rely on it. Future versions of perl might do something different from the version of perl you try it out on. Here be dragons.

from http://perldoc.perl.org/perlsyn.html

Cheers,
Z.

]]> By: Matt S Trout http://www.dangoldin.com/2008/05/30/interesting-perl-behavior/comment-page-1/#comment-3 Matt S Trout Tue, 05 Aug 2008 16:11:40 +0000 http://www.dangoldin.com/blog/?p=17#comment-3 That's a -sort of- bug. perl 5.10 actually throws a warning when you trip it, and provides a 'state $x' keyword that provides the same functionality as 'my $x if 0' safely. The basic problem is that the 'my' causes a lexical pad entry to be generated at compile time, but because the if 0 prevents the statement running at runtime it doesn't get reinitialised on your way round the loop. That’s a -sort of- bug.

perl 5.10 actually throws a warning when you trip it, and provides a ‘state $x’ keyword that provides the same functionality as ‘my $x if 0′ safely.

The basic problem is that the ‘my’ causes a lexical pad entry to be generated at compile time, but because the if 0 prevents the statement running at runtime it doesn’t get reinitialised on your way round the loop.

]]> By: Ricardo http://www.dangoldin.com/2008/05/30/interesting-perl-behavior/comment-page-1/#comment-6 Ricardo Tue, 05 Aug 2008 16:03:02 +0000 http://www.dangoldin.com/blog/?p=17#comment-6 It seems like something like "(my if (0)) $val = 0" is going on. It's weird. It seems like something like “(my if (0)) $val = 0″ is going on. It’s weird.

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