package Set;
use Moo;

has 'items' => (is => 'ro', default => sub { {  } });

no Moo;

sub has {
    my ($self, $e) = @_;
    exists $self->items->{ $e };
}

sub add {
    my ($self, $e) = @_;

    if ( ! $self->has($e) ) {
        $self->items->{ $e } = 1;
    }
}

1;