{
        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;