#!/usr/bin/perl -w

use strict;

package HistoryObj;

sub new {
	my $class = shift;
	my $self = {
		color => 'blue',
		texture => 'rusty metal',
		taste => 'salt',
	};
	bless($self, $class);
	return $self;
}

##</code><code>##

{
	my %history;

	sub _log {
		my $self = shift;
		my $attrib = shift;
		my $value = $self->{$attrib};
		push @{ $history{$self} }, [ $attrib, $value ];
	}

	sub undo {
		my $self = shift;
		return unless (scalar @{ $history{$self} });
		my ($attrib, $value) = @{ pop @{ $history{$self} } };
		$self->{$attrib} = $value;
	}
}

##</code><code>##

sub color {
	my $self = shift;
	if (@_) {
		$self->_log('color');
		$self->{color} = $_[0];
	}
	return $self->{color};
}

sub texture {
	my $self = shift;
	if (@_) {
		$self->_log('texture');
		$self->{texture} = $_[0];
	}
	return $self->{texture};
}

sub taste {
	my $self = shift;
	if (@_) {
		$self->_log('taste');
		$self->{taste} = $_[0];
	}
	return $self->{taste};
}

sub all {
	my $self = shift;
	my @values = @$self{qw( color texture taste )};
	return join("\t", @values);
}

1;

##</code><code>##

#!/usr/bin/perl -w

use strict;
use HistoryObj;

my $hist = HistoryObj->new();
my $hist2 = HistoryObj->new();

$hist->color('pink');
$hist->texture('cotton candy');
$hist->taste('sweet');
print $hist->all(), "\n\n";

$hist2->color('beet purple');
$hist2->texture('slimy round goo');
$hist2->taste('do not ask!');
print $hist2->all(), "\n\n";

for (1 .. 3) {
    $hist->undo();
    print $hist->all(), "\n\n";
}

for (1 .. 3) {
    $hist2->undo();
    print $hist2->all(), "\n\n";
}