{ 
    my( $x, $y ) = ( 0, 0 ); 
    sub t : lvalue { my $ref = (rand >.5) ? \$x : \$y; $$ref } 
    sub showme{ print "x=$x : y=$y" } 
}

t = 5; showme;
x=0 : y=5

t = 7; showme;
x=0 : y=7

t = 9; showme;
x=9 : y=7