#---Sample.pm---
package Sample;

use warnings;
use strict;

use overload( '+'	=> \&add,
		fallback => 1, );

sub TIESCALAR
{
	my $class = shift;
	my $self = { data => [@_], };
	bless( $self, $class );
	return $self;	
}

sub add
{
	$_ .= $_[1] foreach( @{$_[0]->{data}} );
}

sub STORE
{
	@{$_[0]->{data}} = (ref( $_[1] ) eq 'ARRAY') ? @{$_[1]}: ($_[1]);
}

sub FETCH
{
	return $_[0];
}

1;
#---------------

##</code><code>##

#----code.pl----
use warnings;
use strict;

use Sample;

my $var1;
my $var2 = tie( $var1, 'Sample', 'black', 'white' );

# The assigment test...
#$var1 = 'green';
#$var2 = ['green','red'];

# The overload test...
#$var1 + ' bishop';
#$var2 + ' bishop';

#print ref($var2),"\n";
print join( "\n", @{$var2->{data}} );

exit 0;
#---------------

##</code><code>##

Useless use of addition (+) in void context at code.pl line 28.
Argument " bishop" isn't numeric in addition (+) at code.pl line 28.