Liz

Why the question mark? Tie::IxHash is the canonical module for this kind of job.

As an interesting sidenote to the OP: (s)he pretty much described how it works:

I could sorta do it with a pair of arrays and an index variable, but I like being able to reference an element by its key.

Well: the object behind the tied hash comprises of a pair of arrays, one for the keys and one for the values, and a hash, which points towards the index in these arrays for any key.

An alternative implementation, which would likely be a little more compact, would be to use just one hash and one array. For example, the hash could work in the normal way, and the array would contains the ordered keys. But there are other schemes.

Take a look at Tie::IxHash. In case you are interested in doing something by yourself, I did some before:

package OrderedHash;
use strict;

sub new {
   my $self = {};
   $self->{INDEX} = {};
   $self->{PAIRS} = [];
   bless $self;
   return $self;
}

sub set {
   my ($self, $key, $value) = @_;
   push @{$self->{PAIRS}}, $key;
   $self->{INDEX}->{$key} = $#{$self->{PAIRS}};
   push @{$self->{PAIRS}}, $value;
}

sub get {
   my ($self, $key) = @_;
   return $self->{PAIRS}->[$self->{INDEX}->{$key} + 1];
}

sub list_in_order {
   my $self = shift;
   my $is_key = 1;
   foreach (@{$self->{PAIRS}}) {
      if (!$is_key) {
          print "$_\n";
      } else {
          print "[$_] = ";
      }
      $is_key = !$is_key;
   }
}

1;

use OrderedHash;
use Data::Dumper;
use strict;

my $oh = new OrderedHash;
$oh->set("a", 1);
$oh->set("b", 2);
$oh->set("c", 3);
print Dumper($oh);
$oh->list_in_order;
[download]

If you think of your consideration process as a balance sheet, on the positive side, you get an ordered hash. On the negative side, you get a less speed efficient and less memory efficient hash. You trade speed and memory for convenience. That may be a worthwhile trade for you. Or it might be a dealbreaker. Just as long as you're aware of the issues, you can make the right decision for your particular situation.

"I could sorta do it with a pair of arrays and an index variable, but I like being able to reference an element by its key."

my @people = (
   { name => 'John Doe',    age => 30 },
   { name => 'Sally Smith', age => 42 },
);
[download]

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)