3.4 Dropping Those Braces

Most of the time, the dereferenced array reference is contained in a simple scalar variable, such as @{$items} or ${$items}[1]. In those cases, the curly braces can be dropped, unambiguously, forming @$items or $$items[1].

However, the braces cannot be dropped if the value within the braces is not a simple scalar variable. For example, for @{$_[1]} from that last subroutine rewrite, you can't remove the braces.

This rule also means that it's easy to see where the "missing" braces need to go. When you see $$items[1], a pretty noisy piece of syntax, you can tell that the curly braces must belong around the simple scalar variable, $items. Therefore, $items must be a reference to an array.

Thus, an easier-on-the-eyes version of that subroutine might be:

sub check_required_items {
  my $who = shift;
  my $items = shift;
  my @required = qw(preserver sunscreen water_bottle jacket);
  for my $item (@required) {
    unless (grep $item eq $_, @$items) { # not found in list?
      print "$who is missing $item.\n";
    }
  }
}

The only difference here is that the braces were removed for @$items.