use strict;
use warnings;
use IO::File;
use IO::String;

push @IO::File::ISA, 'CommonHandle';
push @IO::String::ISA, 'CommonHandle';

my $fh = IO::File->new;
my $sh = IO::String->new;

$fh->readbuffer;
$sh->readbuffer;

sub CommonHandle::readbuffer{
    my $self = shift;
    print ref $self, "\n";
}