public class LinkedHashSet<G> : Gee.HashSet<G> {
    Gee.List<G> elements = new Gee.LinkedList<G> ();

    public LinkedHashSet (owned Gee.HashDataFunc? hash_func = null, owned Gee.EqualDataFunc? equal_func = null) {
        base ((owned)hash_func, (owned)equal_func);
    }

    public new G get (int index) {
        return elements[index];
    }

    public new void set (int index, G item) {
        var old_item = elements[index];
        if (equal_func (old_item, item)) {
            return;
        }

        elements[index] = item;
        base.remove (old_item);
        base.add (item);
    }

    public override bool add (G item) {
        return base.add (item) && elements.add (item);
    }

    public int index_of (G item) {
        return item in this ? elements.index_of (item) : -1;
    }

    public void insert (int index, G item) {
        if (item in this) {
            return;
        }
        elements.insert (index, item);
        base.add (item);
    }

    public override bool remove (G item) {
        return base.remove (item) && elements.remove (item);
    }

    public G remove_at (int index) {
        var item = elements.remove_at (index);
        base.remove (item);

        return item;
    }

    public Gee.List<G>? slice (int start, int stop) {
        return elements.slice (start, stop);
    }

    public void sort (owned CompareDataFunc? compare_func = null) {
        elements.sort ((owned)compare_func);
    }

    public override Gee.Iterator<G> iterator () {
        return elements.iterator ();
    }
}

void main (string[] args) {
    var l = new LinkedHashSet<Object> ();
    l.add(new Object ());

    var o = l[0];  // this results in g_object_unref: assertion `G_IS_OBJECT (object)' failed
}