class.pl

use strict;
use warnings;

package ClassA;
sub initialize { "A" }

package ClassB;
use base qw(ClassA);
sub initialize { 
    my $class = shift;
    $class->SUPER::initialize . "B";
    # &{ $class . "::SUPER::initialize"}() . "B"; # X?
}

package main;

print  ClassB->initialize;