Numeric Variable Names With Leading Zeroes
Over on the p5p mailing list, a user raised the issue that use of variable $00 is an error starting with Perl 5.32, and asked that this "regression" be fixed.
I have always understood that variables whose names begin with anything but an alphabetic or an underscore are reserved to Perl, and you mess with them at your peril. And this is the gist of the Porters' response to the post. Recent versions of perlvar say this explicitly, though earlier versions of that document restrict themselves to describing currently-implemented special variables.
For what it's worth, perl532delta appears not to mention this as a new diagnostic.
I wondered how much of this kind of thing was in CPAN, so I whipped up a Perl::Critic policy to try to find them: Variables::ProhibitNumericNamesWithLeadingZero. I then ran this against CPAN as it stood July 23 2022.
The only violation of this policy that I found was in line 1209 of Net::Elexol::EtherIO24. The most recent release of this module (as of this writing) is August 11 2009. The line in violation (in context) is
1208 $txt .= sprintf("MAC: %02.2x:%02.2x:02.2x:02.2x:02.2x:02.2x ".
1209 "Fw: %02.2x.$02.2x",
1210 unpack("x$len CCCCCCCC", $cmd));
and looks to me very much like a typo for %02.2x. The distribution requires a threaded Perl, and CPAN Testers show failures with Error: Numeric variables with more than one digit may not start with '0' at Net-Elexol-EtherIO24-0.22-0/blib/lib/Net/Elexol/EtherIO24.pm line 1209. for Perl versions 5.32.1 and above. There are no reports for 5.32.0.
Under the circumstances I can not imagine anyone (other than maybe the original poster on p5p) actually wanting this perlcritic policy published, but I did stick it on GitHub for the curious.
I blog about Perl.
Why not publish it? It's valid, no? Or is running it just a waste of time since it's a syntax error?
The policy is valid as far as I know. No false positives, at least.
My bias toward non-publication (beyond GitHub) is because it does not address a current problem, and it appears to me that the single instance of this in CPAN is a typographical error.
The one argument I can think of in favor of publication to CPAN is that maybe someone wants to clean up a code base, perhaps prior to a Perl upgrade.
Published Perl::Critic::Policy::Variables::ProhibitNumericNamesWithLeadingZero. I figured when the lead article of this week's Perl Weekly alludes to it I kind of have to.