sub new {
    my($proto, $fields) = @_;
    my($class) = ref $proto || $proto;
    my $self = bless [], $class;
    ...

##</code><code>##

sub new
  {
  my $proto = shift @_;
  my $self = { @atom_fields, @_ };
  $self = bless ($self, ref($proto) || $proto);
  ...

##</code><code>##

sub new {
    my($proto, $fields) = @_;
    my($class) = ref $proto || $proto;

    $fields = {} unless defined $fields;

    # make a copy of $fields.
    bless {%$fields}, $class;
}