my $class = shift; # at the top of the function
return bless \@deck, $class; # at the bottom

##</code><code>##

use List::util; # use the module but do not import shuffle

# ...

sub shuffle {
  my $deck = shift;
  my $out = wantarray ? [] : $deck;
  @$out = List::Util::shuffle(@$deck);
  return wantarray ? @$out : $out;
}