#! perl
use strict;
use warnings;
$| = 1;

#------------------------------------------------------------------------------
package Phaser;

sub new
{
    my ($class, $name) = @_;
    my  $self = {};
    $self->{name} = $name;
    return bless $self, $class;
}

#------------------------------------------------------------------------------
package Dalek;

sub new
{
    my ($class, $phaser_ref) = @_;
    my  $self = {};
    $self->{phaser} = $phaser_ref;
    return bless $self, $class;
}

sub exterminate
{
    return 'Firing phaser ' . $_[0]->{phaser}->{name} . "\n";
}

sub obey
{
    return 'obey';
}

sub DESTROY
{
    my ($self) = @_;
    print 'DESTROYing a Dalek (phaser is ', $self->{phaser}->{name}, ")\n";
    $self->{phaser}->{name} = 'Obliterator';
}

#------------------------------------------------------------------------------
package main;

my $phaser = Phaser->new('Exterminator');
my $enemy  = Dalek ->new($phaser);

print 'My enemy is a ',        ref $enemy,
      ' with a phaser named ', $phaser->{name}, "\n";
print $enemy->exterminate();

print 'My enemy must ', $enemy->obey(),
       undef($enemy),
      '. His phaser is named ', $phaser->{name},
       eval('$enemy->exterminate()'),
      ". Bye!\n"; 
print $@ if $@;

print 'The phaser is named ', $phaser->{name}, "\n";

##</code><code>##

16:59 >perl 552_SoPW.pl
My enemy is a Dalek with a phaser named Exterminator
Firing phaser Exterminator
Use of uninitialized value in print at 552_SoPW.pl line 67.
My enemy must obey. His phaser is named Exterminator. Bye!
DESTROYing a Dalek (phaser is Exterminator)
Can't call method "exterminate" on an undefined value at (eval 1) line 1.
The phaser is named Obliterator
16:59 >