package A;

sub new { bless {}, shift }
sub foo { 'A' }

sub bar {
   my $self = shift;

   print '$self->foo() = ', $self->foo(), "\n";
   print 'foo( $self ) = ', foo( $self ), "\n";
}

package B;

our @ISA = ('A');
sub foo { 'B' }

package main;

my $obj_a = A->new();
my $obj_b = B->new();

print "object A call to bar():\n";
$obj_a->bar();
print "object B call to bar():\n";
$obj_b->bar();
__END__
object A call to bar():
$self->foo() = A
foo( $self ) = A
object B call to bar():
$self->foo() = B
foo( $self ) = A