public IReadOnlyList <TItem> GetOrAdd(TKey key, Func <TKey, IEnumerable <TItem> > getFunc)
{
int index = Primary.GetOrAdd(key, k =>
{
var rawList = getFunc(k);
lock (Primary)
{
int[] itemListByIndex = rawList.Select(item =>
{
if (!ItemDict.TryGetValue(item, out int itemIndex))
{
itemIndex = ItemList.Count;
ItemList.Add(item);
ItemDict[item] = itemIndex;
}
return(itemIndex);
}).ToArray();
var intArray = new IntArray(itemListByIndex);
if (!ListDict.TryGetValue(intArray, out int listIndex))
{
lock (ListList)
{
listIndex = ListList.Count;
ListList.Add(itemListByIndex.Select(ii => ItemList[ii]).ToArray());
}
ListDict[intArray] = listIndex;
}
return(listIndex);
}