ch16.003_prob_ex16.1

Perl Best Practices the source code

##############################################################################
## Example 16.1 (NOT RECOMMENDED) from Chapter 16 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 16-1. Making a hash of your psyche


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


# Generic base class confers an ID number and description attribute
# on all derived classes...
package Object;
 
# Class attribute...
my $next_id = 1;
 
# Constructor expects description as argument, 
# and automatically allocates ID number...
sub new {
    my ($class, $arg_ref) = @_;
 
    # Create object representation...
    my $new_object = bless {}, $class;
 
    # Initialize attributes...
    $new_object->{ id } = $next_id++;
    $new_object->{desc} = $arg_ref->{desc};
 
    return $new_object;
}
 
# and later...
 
# Derived class for psychological modelling...
package Psyche;
 
# All instances need ID and description...
use base qw( Object );
 
# Constructor expects to be passed an ego representation,
# but generates other psychological layer automatically...
sub new {
    my ($class, $arg_ref) = @_;
 
    # Call base-class constructor to create object representation 
    # and initialize identity attributes...
    my $new_object = $class->SUPER::new($arg_ref);
 
    # Initialize psyche-specific attributes...
    $new_object->{super_ego} = Ego::Superstructure->new();
    $new_object->{   ego   } = Ego->new($arg_ref->{ego});
    $new_object->{   id    } = Ego::Substrate->new();    # Oops! Reused 'id' entry
 
    return $new_object;
}
 
# Summarize a particular psyche...
sub describe{
    my ($self) = @_;
 
    # List case number...
    print "Case $self->{id}...\n";
 
    # Describe pschological layers...
    $self->{super_ego}->describe();
    $self->{   ego   }->describe();
    $self->{   id    }->describe();
 
    return;
}
 
# and later still...
 
my $psyche = Psyche->new({ desc=>'me!', ego=>'sum' });
 
$psyche->{id} = 'est';

use Data::Dumper 'Dumper';
warn Dumper [ $psyche ];


package Ego::Superstructure;

sub new {
    return 1;
}

package Ego;

sub new {
    return 1;
}

package Ego::Substrate;

sub new {
    return 1;
}