After a long and helpful discussion in the Chatterbox,
I hacked this together. It's a base class which lets you
build a hash that fills itself 'on demand'.
#! /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};