package Bar;

sub new { ... }

sub foo {
  state $bar;
  $bar++;
  return $bar;
}

##</code><code>##

$bar1 = Bar->new();
$bar2 = Bar->new();

$bar1->foo(); # returns 1, as you would expect
$bar1->foo(); # returns 2, as you would expect
$bar2->foo(); # returns 3, possibly unexpected