Specializing attributes

package Number;
use Moose;

has 'num' => ( is => 'ro', isa => 'Num' );

sub round { ... }

package Integer;
use Moose;
extends 'Number';

has '+num' => ( isa => 'Int' );

sub is_prime { ... }

• Here we extend A's num with our +num.
• Restrictions apply, cannot make things more general, only more specific.