sub _delegate {
      # this is not a complete method.  It's just here for illustration
      my ($self, $slot, $object) {
      $self->{$slot}{object} = $object;
      my @missing;
      foreach my $method (@{$self->{$slot}{methods}}) {
          push @missing => $method unless UNIVERSAL::can($object, $method);
      }
      die "Interface required @missing" if @missing;
      return $self;
  }