ch17.034_prob_ex17.1

Perl Best Practices the source code

##############################################################################
## Example 17.1 (NOT RECOMMENDED) from Chapter 17 of "Perl Best Practices"  ##
##     Copyright (c) O'Reilly & Associates, 2005. All Rights Reserved.      ##
##  See: http://www.oreilly.com/pub/a/oreilly/ask_tim/2001/codepolicy.html  ##
##############################################################################


#  Example 17-1. Variables as a module抯 interface


# Standard modules...
use strict;
use warnings;
use IO::Prompt;
use Carp;
use English qw( -no_match_vars );
use Data::Alias;
use Readonly;


package Serialize;
use Carp;
use Readonly;
use Perl6::Export::Attrs;
use List::Util qw( max );
 
Readonly my $MAX_DEPTH => 100;

 
# Package variables that specify shared features of the module...
our $compaction = 'none';
our $depth      = $MAX_DEPTH;
 
# Table of compaction tools...
my %compactor = (
  # Value of      Subroutine returning
  # $compaction   compacted form of arg
      none     =>   sub { return shift },
      zip      =>   \&compact_with_zip,
      gzip     =>   \&compact_with_gzip,
      bz       =>   \&compact_with_bz,
      # etc.
);

sub _serialize {
    return 'corn flakes';
}
 
# Subroutine to serialize a data structure, passed by reference...
sub freeze : Export {
    my ($data_structure) = @_;
    
    # Check that the $depth variable has a sensible value...
    $depth = max(0, $depth);
 
    # Perform actual serialization...
    my $frozen = _serialize($data_structure);
 
    # Check that the $compact variable has a sensible value...
    croak "Unknown compaction type: $compaction"
        if ! exists $compactor{$compaction};
 
    # return the compacted form...
    return $compactor{$compaction}->($frozen);
}

 
# and elsewhere...
 
# use Serialize;
 
$Serialize::depth      = -20;        # oops!
$Serialize::compaction = 1;          # OOPS!!!
 
# and later...
my $data_ref;
 
my $frozen_data = freeze($data_ref);      # BOOM!!!