sub half {
  my $number; 
  if (ref($_[0]) eq 'MyPackage') {
      my $self   = shift();
      $number = shift();
   } else {
       $number = shift();
   }
   return $number / 2;
}

##</code><code>##

sub half {

  if (ref($_[0]) =~ /MyPackage/ ) { my $self = shift; } 

# as the former Perl4-like functions donīt need the $self object, this line's role is to clean up the first element of the @_ array! And, so, make things ready for the shifts your code already is set to!
  
  my $number = shift;
  
  return $number / 2;
  
}