public override Slice EncodeComposite(FdbTuple <T1, T2> key, int items)
                {
                    switch (items)
                    {
                    case 2: return(key.ToSlice());

                    case 1: return(FdbTuple.Pack <T1>(key.Item1));

                    default: throw new ArgumentOutOfRangeException("items", items, "Item count must be either 1 or 2");
                    }
                }