Hash::Compact - A hash-based object implementation with key alias and default value support


  package My::Memcached;

  use strict;
  use warnings;
  use parent qw(Cache::Memcached::Fast);

  use JSON;
  use Hash::Compact;

  my $OPTIONS = {
      foo => {
          alias_for => 'f',
      bar => {
          alias_for => 'b',
          default   => 'bar',

  sub get {
      my ($self, $key) = @_;
      my $value = $self->SUPER::get($key);
      Hash::Compact->new(decode_json $value, $OPTIONS);

  sub set {
      my ($self, $key, $value, $expire) = @_;
      my $hash = Hash::Compact->new($value, $OPTIONS);
      $self->SUPER::set($key, encode_json $hash->compact, $expire);

  package main;

  use strict;
  use warnings;
  use Test::More;

  my $key   = 'key';
  my $value = { foo => 'foo' };
  my $memd  = My::Memcached->new({servers => [qw(localhost:11211)]});
     $memd->set($key, $value);

  my $cached_value = $memd->get($key);
  is        $cached_value->param('foo'), 'foo';
  is        $cached_value->param('bar'), 'bar';
  is_deeply $cached_value->compact, +{ f => 'foo' };

  $cached_value->param(bar => 'baz');
  $memd->set($key, $cached_value->compact);

  $cached_value = $memd->get($key);
  is        $cached_value->param('foo'), 'foo';
  is        $cached_value->param('bar'), 'baz';
  is_deeply $cached_value->compact, +{ f => 'foo', b => 'baz' };



When we store some structured value into a column of a relational database or some key/value storage, redundancy of long key names can be a problem for storage space.

This module is yet another hash-based object implementation which aims to be aware of both space efficiency and easiness to use for us.


new (\%hash [, \%options])

  my $hash = Hash::Compact->new({
          foo => 'foo',
      }, {
          foo => {
              alias_for => 'f',
          bar => {
              alias_for => 'b',
              default   => 'bar',

Creates and returns a new Hash::Compact object. If \%options not passed, Hash::Compact object $hash will be just a plain hash-based object.

\%options is a hash-ref which key/value pairs are associated with ones of \%hash. It may contain the fields below:

  • alias_for

    Alias to an actual key. If it's passed, \%hash will be compacted into another hash which has aliased key. The original key of \%hash will be just an alias to an actual key.

  • default

    If this exists and the value associated with the key of \%hash is undefined, Hash::Compact object $hash returns just the value. It's for space efficiency; $hash doesn't need to have key/value pair when the value isn't defined or it's same as default value.

param ($key)

param (%pairs)

  $hash->param('foo');          #=> 'foo'
  $hash->param('bar');          #=> 'bar' (returns the default value)

      bar => 'baz',
      qux => 'quux',
  $hash->param('bar');          #=> 'baz'

Setter/getter method.

compact ()

  my $compact_hash_ref = $hash->compact;
  #=> { f => 'foo', b => 'baz' qux => 'quux' } (returns a compacted hash)

Returns a compacted hash according to \%options passed into the constructor above;

to_hash ()

This method will be deprecated and removed at later version.

keys ()

  @keys = $hash->keys; #=> (foo, bar, qux)

Returns the original key names. If default option is set for a key, the key will be returned even if the value associated with the key is not set.

original ()

  my $original_hash_ref = $hash->original;
  #=> { foo => 'foo', bar => 'baz' qux => 'quux' } (returns an original hash)

Returns the original key-value pairs as HashRef, which includes key-value pairs if the key-values not set but default option is designated.


Kentaro Kuribayashi <>



Copyright (C) Kentaro Kuribayashi

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.