$ ./test.pl
score: 0
vx: -1
symbol: _

##</code><code>##

shown: 1
score: 0
x: 0
vx: -1
y: 0
vy: 0
symbol: _

##</code><code>##

#!/usr/local/bin/perl
package Object;
use strict;

sub new {
	my ($proto, %args) = @_;
	my $class = ref $proto || $proto;
	my $self = bless {}, $class;
	$self->init(\%args);
	return $self;
}

sub init {
	my ($self, $args) = @_;
	my $defaults=$self->defaults;

	if (ref($defaults)) {
		# This is technically Ok because you are getting
		# defualts from yourself and accordingly the key=>values
		# should be correct
		@{$self}{keys %$defaults}=@{$defaults}{keys %$defaults};
	}
	# If %args are given to new(), use those instead
	# Unfortunately this is technically bad practice, as the
	# key=>values will not be coming from yourself (in an abstract sense)
	# accordingly you really should implement code to determine if
	# the passed keys are in the set of allowed keys.
	# one way to do this is to make method calls for all legal attributes
	# and then use the keyname as the methodname. If the arg is not legal
	# perl will throw a runtime error that the method is not found
	# leaving it as is is asking for hard to identify bugs.
	# something like this might be in order:
	#    $self->$_($args->{$_}) foreach keys %$args;

	@{$self}{keys %$args}=@{$args}{keys %$args};
	return $self;
}

1;


package Mover;
#use Object;
our @ISA = qw(Object);
use strict;

sub defaults {
	my $self=shift;
	my $defaults = {
		'symbol' => '?',     # override this in subclasses
		'x'      => 0,       # x-coordinate
		'y'      => 0,       # y-coordinate
		'vx'     => 0,       # velocity in x-direction
		'vy'     => 0,       # velocity in y-direction
		'shown'  => 1,       # still alive?
	}
}

1;


package Player;
#use Mover;
use strict;
our @ISA = qw(Mover);

sub defaults {
	my $self=shift;
	my $defaults =$self->SUPER::defaults();
	@{$defaults}{'symbol','score'}=('_',0);
	return $defaults;
}

1;
use strict;
use warnings;
#use Player;
my $player = Player->new('vx' => -1);
for (keys %$player) {
	print "$_: ", $player->{$_}, $/;
}

1;