package Tie::HashDefaultValue;
require Tie::Hash;
@ISA = 'Tie::ExtraHash';
use strict;

sub TIEHASH {
  my ($class, $default) = @_;
  return bless [{}, $default], $class;
}

sub FETCH {
  my ($tied, $key) = @_;
  if (exists $tied->[0]{$key}) {
    return $tied->[0]{$key};
  }
  else {
    return $tied->[1];
  }
}

1;

##</code><code>##

tie my %bar, 'Tie::HashDefaultValue', sub {};
# time passes
$bar{foo}->();

##</code><code>##

sub FETCH { exists $_[0][0]{$_[1]} ? $_[0][0]{$_[1]} : $_[0][1] }