use Perl

• Got a similar problem (Score:2)

  by BooK (2612) <{book} {at} {cpan.org}> on 2004.05.04 7:01 (#30554) Homepage Journal

  I had to do someting similar to create a multilevel hash table that returns a list of "cached" things given a list of parameters that represent the hashing value.

  The main problem was not creating the various anonymous hashes, but that the last item is not a {} but a []. The trick was to keep a reference to the previous step, to be able to go back and turn a newly created hash reference into an anonymous array.

  # $thing is a hash reference
  # @keys is the list of $thing attributes I'm using for the hashing algorithm
  # $hashtable is a reference to the hash table itself
  my $list = $hashtable;
  my $last;
  ($last, $list) = ( $list, $list->{$thing->{$_}} ||= {} ) for @keys;
  $list = $last->{$thing->{$keys[-1]}} = [] if ref $list eq 'HASH';
  # and now $list points to the list of interesting items
  # which was created (empty) if needed

  Using $list, $last adds extra obfuscation points, but that wasn't intended, since those are fitting names.

  Reply to This