my ($class, $whatever) = @_;
  my %params = (); # new params to use instead of parent's params
  my $this = new base_class; # create a new parent, and 
                             # let it set its own defaults
  # clobber the base_class' defaults:
  while (my ($k,$v) = each %params) {
     $this->{$k} = $v;
  }
  bless($this, $class); # re-bless into the current package