#! /usr/bin/perl -w

package Tie::AutoCache;

use strict;
use vars qw(@ISA);

use Tie::Hash;

@ISA = qw(Tie::StdHash);

sub TIEHASH {

  my($class) = shift;
  my($self) = { };
  bless $self, $class;
}

sub FETCH {

  my($self, $key) = @_;

  unless (exists $self->{$key}) {
    if ($self->can($key)) {
      $self->{$key} = $self->$key();
    }
    else {
      warn "No method for '$key'";
      $self->{$key} = undef;
    }
  }
  return $self->{$key};
}

1;

#########################################################

package Thingy;

use vars qw(@ISA);

@ISA = qw(Tie::AutoCache);

sub new {

  my($class) = shift;
  my(%hash);
  tie %hash, $class;
  return \%hash;
}

sub foo {

  my($self) = @_;
  $self->{bar} = "this is bar\n";
  return "this is foo\n";
}

1;

#########################################################

package main;

my($thingy) = new Thingy();

print $thingy->{foo};
print $thingy->{bar};
print $thingy->{not};