package Foo;

sub new {
  my ($class) = @_;
  return bless [], $class;
}

sub val {
  my $self = shift;
  $self->[0] = $_[0] if @_;
  "Foo($self->[0])";
}

package Bar;

sub new {
  my ($class) = @_;
  return bless { val => 'nothing' }, $class;
}

sub val {
  my $self = shift;
  $self->{val} = $_[0] if @_;
  "Bar($self->{val})";
}