package XXX;

my %already_created_objects;

sub new {
	my ($class, $X) = @_;
	if (!$already_created_objects{$X}) {
		$already_created_objects{$X} = bless {somekey => $X} $class;
	}
	$already_created_objects{$X}
}

##</code><code>##

...
$obj = new XXX($some_var_which_can_repeat);
...
if ($some_conditions) {
	some_superundef $obj
}
...