package Pseudo;
# ---------------------------------------------------------
sub new {
  my ($proto) = shift;

  unless (defined $proto){
    die "ERROR: 'new' must be called as a class- or object-method\n";
  }

  my $self = [{}];

  if (ref $proto){ # call cloning constructor if needed
    return $proto->clone();
  } # if

  else { # normal constructor; don't copy data
    bless ($self, $proto);
  } # else

  return ($self);
} # new
# ---------------------------------------------------------
sub clone {
  my ($proto) = shift;

  if (__PACKAGE__ eq ref $proto){
    my $self = [{}];
    bless ($self, ref $proto);

    foreach (keys %$proto){ # copy keys, but not values
      $self->AddKey($_);
    } # foreach

    return ($self);
  } # if

  else {
    die "ERROR: 'clone' must be called as an object method\n";
  } # else

} # clone
# ---------------------------------------------------------
sub AddKey {
  my ($self, $key) = @_;

  if (exists $self->[0]->{$key}){
    $DEBUG and warn "WARNING: Key $key already existing\n";
    $self->{$key} = undef; # clear field
  } # if

  else {
    my $nextFreeIndex = scalar( keys %{ $self->[0] } ) + 1;
    $self->[0]->{$key} = $nextFreeIndex; # add key
#   $self->[$nextFreeIndex] = undef;
  } # else

  return $self;
} # AddKey