package Super::Class;

my $class_indexes = {};

sub NEXT_IDX {
	my $class = shift;
	#if we have an index for this class, then return it
	if (defined $class_indexes->{$class}) {
		return ++$class_indexes->{$class};
	}
	else {
		no strict 'refs';
		my @isa = @{$class . "::ISA"};
		#root class has no super
		my $idx = @isa ? $isa[0]->CURR_IDX() : -1;
		$class_indexes->{$class} = $idx + 1;
		return $class_indexes->{$class};
	}
}

sub CURR_IDX {
	my $class = shift;
	return $class_indexes->{$class};
}

use constant FOO_IDX => __PACKAGE__->NEXT_IDX(); # 0
use constant BAR_IDX => __PACKAGE__->NEXT_IDX(); # 1
use constant BAZ_IDX => __PACKAGE__->NEXT_IDX(); # 2

package Other::Sub::Class;
BEGIN {our @ISA = qw(Super::Class)};

use constant DIFFERENT_IDX => __PACKAGE__->SUPER::NEXT_IDX();
#set to 3

package Sub::Class;
BEGIN {our @ISA = qw(Super::Class)};

use constant OTHER_IDX => __PACKAGE__->SUPER::NEXT_IDX();
#also set to 3