| AddOrGetTKey, TValue(IDictionaryTKey, TValue, TKey, TValue) | Adds the specified key and value to the specified IDictionaryTKey, TValue if the key does not already exist, and returns the value. |
| AddOrGetTKey, TValue(IDictionaryTKey, TValue, TKey, FuncTKey, TValue) | Adds the specified key and value to the specified IDictionaryTKey, TValue if the key does not already exist, and returns the value. |