private static void FillIndex <TIndexKey>(IIndex <TIndexKey, int> index, [NotNull] FastCollection <TRaw> fastCollection, [NotNull] Func <TRaw, TIndexKey> selector)
        {
            var indexData = new List <IndexItem <TIndexKey, int> >();

            foreach (var item in fastCollection.Items)
            {
                indexData.Add(new IndexItem <TIndexKey, int>(selector(item.Data), item.Id));
            }
            index.FillIndex(indexData);
        }