sub add_method {
   my $self = shift;
   my $name = shift;
   die unless $name and $name =~ /^\w+$/;
   my $sub = sub {
           my $self = shift;
           my $item = $name;
           return [ @{ $self->{items} }, $item ];
   };
    no strict 'refs';
    *{$name} = $sub;
}