package A;
sub new { 
    my ($class, %args) = @_; 
    bless \%args, $class;
}

# access foo
sub _foo {
    return shift->{foo};
}

sub printFoo {
    my $self = shift;
    return $self->_foo;
}

package B;
@B::ISA = qw/ A /;

# access foo OVERLOAD
sub _foo {
    return shift->{foo} + 1;
}

package main;

my $ob = B->new( foo => 23 );
print $ob->printFoo; # A: 23, B: 24