our

• IMHO, generally used in the wrong way

• Package private variables can in most cases be declared with my

      package TwoFlowers;
      my $config;

our

• Global variables used only once can be placed in a no strict block

      {   no strict 'vars';
          $VERSION = '1.23';
          @ISA = qw(Flower);
      }

• Public variables can be declared with use vars

      use vars qw($DEBUG);

open()

• Very protean syntax with several different modes

• Most part of it here since a long time

• But two recent additions are commonly used

open(FILEHANDLE, $path) vs open my $fh, $path

• Solution: manually create the file handle

      use FileHandle;
  
      open my $fh = new FileHandle, $path or die $!;

• or, even better, go the OO way

      use FileHandle;
  
      my $fh = FileHandle->new($path) or die $!;

3-arguments open()

• Unfortunately, the following obvious code doesn't work :-(

      my @args = ('>', $path);
      open($fh, @args);

• Simple solution: transform it back to 2-arguments open()

      open($fh, '<'.$path);

• Caveat: loosing the protecting feature

3-arguments open()

• Second solution: FileHandle (since 5.002), or IO::File (since 5.003_07)

      use FileHandle;
      my $fh = FileHandle->new($path, $mode);
      # where $mode is ANSI mode: r, w, r+, etc

v-strings

• Syntax introduced with Perl 5.6

• Any usage for anything other than version number should be verboten

• Haven't encountered any v-strings yet

v-strings

• Solution: get back to strings or floats

  • Pro: well-known method, used since years

  • Con: less reliable

  • Example:

        if ($version > 2.034) {
            ...
        }

v-strings

• Solution: use version.pm (works with 5.005_04 and later, core in 5.10)

  • Pro: object interface with overloaded operators

  • Con: doesn't provide much portability beyond 5.6

  • Example:

        use version;
    
        my $vers1 = version->new("1.2.3");
        my $vers2 = version->new("1.2.5");
    
        if ($vers1 < $vers2) {
            ...
        }

v-strings

• Solution: use Perl::Version (pure Perl, works with at least 5.004)

  • Pro: classic object module, good for modifying versions

  • Con: must numify to compare versions

  • Example:

        use Perl::Version;
    
        my $vers1 = Perl::Version->new("1.2.3");
        my $vers2 = Perl::Version->new("1.2.5");
    
        if ($vers1->numify < $vers2->numify) {
            ...
        }

qr//

• Syntax introduced with Perl 5.005

• Often seen in test suites

  • Typical use: like($result, qr/regexp/)

  • Can be safely replaced with a simple string with no functional risk

• When used in actual code

  • ...

  • Haven't seen the case yet :-)

  • But should be as safe as inside tests

Assertions

• \z (Perl 5.006)

  • \Z matches only at end of string, or before newline at the end

  • \z matches only at end of string

• Will be seen as a "z" by Perl 5.004

• Therefore must protect the use of this assertion

      my $end = $] >= 5.005 ? "\\z" : "\\Z";
  
      substr($path, 0, -$ignore) =~ s/X(?=X*$end)/$CHARS[int(rand($#CHARS))]/ge;

Classes

• POSIX classes [:class:] (Perl 5.6)

  • Solution: replace these by their explicit equivalent, see perlre

• Unicode classes (Perl 5.6)

   \x{263a}  wide hex character
   \N{nom}   named character

   \pP  Match P, named property. Use \p{Prop} for longer names.
   \X   Match eXtended Unicode "combining character sequence",
        equivalent to (?:\PM\pM*)
   \C   Match a single C char (octet) even under Unicode.

  • Abandon all hope

Extended patterns

• (?#text) (Perl 5.003)

• (?imsx-imsx) (Perl 5.003)

• (?:pattern) (Perl 5.003)

• (?=pattern) (Perl 5.003)

• (?!pattern) (Perl 5.003)

• (?<=pattern) (Perl 5.005)

• (?<!pattern) (Perl 5.005)

Extended patterns

• (?>pattern) (Perl 5.005, experimental)

• (?(condition)yes-pattern|no-pattern) (Perl 5.005, experimental)

• (?{ code }) (Perl 5.005, experimental)

• (??{ code }) (Perl 5.6, experimental)

warnings

• It is the first cause of incompatibility with old Perls

• However $^W is available since Perl 5.0

• ...

warnings

• It was the first cause of incompatibility with old Perls

• JFDI: warnings-compat

• $CPAN/S/SA/SAPER/warnings-compat-0.04.tar.gz

      $ perl5.00405 -e 'use warnings; warnings::warnif "hello"'
      hello at -e line 1
      $ perl5.00405 -e 'no warnings;  warnings::warnif "hello"'
      $ 

warnings-compat

• Several limitations, but it works

      use warnings::register;
      
      {
          no warnings 'redefine';
          ...
      }
      
      warnings::warnif "...";

• Caveats:

  • Not lexical

  • Categories are not used

warnings

• Other solution: directly use $^W instead

• Example:

      package My::Module;
      local $^W = 1;

base

• Solution: replace it with the equivalent code

      use base qw(Parse::Syslog);

• becomes

      use Parse::Syslog;
  
      {   no strict;
          push @ISA, qw(Parse::Syslog);
      }

base

• Solution: use parent.pm

  • Was discussed and approved on P5P

  • Simple, pure Perl, 5.004 compatible

      package LolPerl;
      sub exclaim { "I CAN HAS PERL" }
  
      package Cheez;
      use parent "LolPerl";