{
	package Voodoo;

	sub FETCH {
		my $self = shift;
		return $self->{'a'};
	}
	
	sub STORE {
		my $self = shift;
		my $val = shift;
		$self->{'a'} += $val;
	}
	
	sub TIESCALAR {
		my $self = {};
		my $class = shift;
		bless $self, $class;
		return $self;
	}
}

my $a;
tie $a, 'Voodoo';

$a = 4;
$a = 2;
$a = 9;

say $a;