# $obj->fooify(1,2,3) or fooify(10,20,30)
# always expects 3 "real" args
sub fooify {
  my $self;
  $self = shift if @_ == 4;  # if 4 args, the first is the object/class
  my ($x, $y, $z) = @_;
  # ...
}

##</code><code>##

sub fooify {
  my $self;
  $self = shift if UNIVERSAL::isa($_[0], __PACKAGE__);
  my ($x, $y, $z) = @_;
  # ...
}