GetOrAdd(TKey, TValue) | Adds a key/value pair to the OrderedDictionaryTKey, TValue if the key does not already exist as an O(1) operation. |
GetOrAdd(TKey, FuncTValue) | Adds a key/value pair to the OrderedDictionaryTKey, TValue by using the specified function, if the key does not already exist as an O(1) operation. |