#!perl
use strict;
use warnings;

use My::Package;
use My::Package::Derived;

local $\ = "\n";

my $item1 = new My::Package;
my $item2 = new My::Package::Derived;

print $item1->SOME_VALUE;
print $item1->SOME_DERIVED_VALUE;
print $item1->ANOTHER_DERIVED_VALUE;

print '-' x 30;

print $item2->SOME_VALUE;
print $item2->SOME_DERIVED_VALUE;
print $item2->ANOTHER_DERIVED_VALUE;

##</code><code>##

package My::Package;
use strict;
use warnings;

use constant SOME_VALUE => 12;
use constant SOME_DERIVED_VALUE => 14;
use constant ANOTHER_DERIVED_VALUE => 21;

sub new {
    bless {}, ref($_[0]) || $_[0];
}

1;

##</code><code>##

package My::Package::Derived;
use strict;
use warnings;
use My::Package;

our (@ISA) = qw[My::Package];

use constant SOME_DERIVED_VALUE => 15;

sub ANOTHER_DERIVED_VALUE() {
    int(rand(100)+1);
}

1;