package Server;
...
sub new {
  ...
  $self = {kiosk=>undef};
  ...
  return $self;
}
sub kiosk {
  my $self = shift;
  my $m = shift;
  if( defined $m ){
    die unless $self->_set_kiosk($m);
  }
  return $self->{kiosk}
}
# returns 0 on failure, 1 on success
sub _set_kiosk {
  my $self = shift;
  my $akiosk = shift;
  if( ! $akiosk->connected() ){ return 0 }
  $self->{kiosk_id} = $akiosk->id();
  print "setting the kiosk to this: " . $akiosk. "\n";
  return 1;
}
sub do_transaction {
  my $self = shift;
  return 0 unless defined $self->{kiosk};
  ...
}