sub initialize {
    return shift->call_super_before(\@_, sub {
	my($self) = @_;
        $self->die($self->get('values'), undef, 'number of elements must be even')
	    unless @{$self->get('values')} % 2 == 0;
	return;
    });
}

##</code><code>##

my($_BAR) = 1;
sub foo {
    return shift->call_super_before(\@_, sub {
        die('gone') unless $_BAR;
        return;
    });
}

##</code><code>##

package T1;
sub s1 {print("T1:s1\n")}

package T2;
use base T1;

package T3;
use base T2;
sub s1 {shift->SUPER::s1}

package main;
no strict 'refs';
exists($T2::{s1}) && die('not here');
T3->s1;
exists($T2::{s1}) && die('here');