use strict;
$^W++;
package A;
use overload '""' => sub { overload::StrVal(shift) . 'xx' };

package B;
@B::ISA = 'A';

package main;

my $a = bless \(my $aa = 'abc'), 'A';
print "$a\n";
bless $a, 'B'; # re-bless
print "$a\n";