# from Extending and Embedding Perl, section 4.5 
$HE = {
       NEXT => $HE_next,
       HEK => {
	       HASH => $hash,
	       LEN => length($key),
	       KEY => $key,
	      }
       VAL => $SV,
      };

##</code><code>##

$elem->delete;
$elem->exists;
$$elem = $x;
print $elem; # overloaded for convenience
print $$elem;

##</code><code>##

use strict;
use warnings;
package Tie::LazyHash;
require Tie::Hash;
our @ISA = 'Tie::StdHash';

sub FETCH {
    Tie::LazyHash::Elem->new( @_ );
}

package Tie::LazyHash::Elem;
use Class::InsideOut qw(id private register);
use Scalar::Util 'weaken';

use overload 'bool' => '_get';
use overload '""' => '_get';
use overload '0+' => '_get';

private _hash => my %hash;
private _key => my %key;

sub _hash;
sub _key;

sub new {
    my ($proto, $hash, $key) = @_;
    my $class = ref $proto || $proto;
    my $self = bless \do{ my $bidding }, $class;
    tie $$self, 'Tie::LazyHash::Elem::Inner', id($self);
    weaken( $hash{id $self} = $hash );
    $key{id $self} = $key;
    register $self;
}

sub _get {
    my $self = shift;
    my $hash = _hash $self;
    return $hash->{_key $self};
}

sub _set {
    my ($self, $val) = @_;
    my $hash = _hash $self;
    $hash->{_key $self} = $val;
}

sub delete {
    my $self = shift;
    my $hash = _hash $self;
    delete $hash->{_key $self};
}

sub exists {
    my $self = shift;
    my $hash = _hash $self;
    exists $hash->{_key $self};
}

sub _hash {
    my $self = shift;
    if (ref $self) {
	$self = id $self;
    }
    return $hash{$self};
}

sub _key {
    my $self = shift;
    if (ref $self) {
	$self = id $self;
    }
    return $key{$self};
}

package Tie::LazyHash::Elem::Inner;

sub TIESCALAR {
    my ($class, $id) = @_;
    bless \$id, $class;
}

sub FETCH {
    my $self = shift;
    Tie::LazyHash::Elem::_get($$self);
}

sub STORE {
    my ($self, $val) = @_;
    Tie::LazyHash::Elem::_set($$self, $val);
}

1;
__END__