Programming Perl 4th : Chapter 9 - Chapter 19

$SIG{QUIT} = "quit_catcher";  # implies "main::quit_catcher"
$SIG{QUIT} = *quit_catcher;   # forces current package's sub

继承用parent了：
package Horse;
use parent qw(Critter);

可以把其他类的子函数借来用用，INVOCANT–>DOES(ROLE)