| Overload | Description | 
|---|---|
| GetOrAdd(TKey,TValue) | Adds a key/value pair to the IDictionary if the key does not already exist. | 
| GetOrAdd(TKey,Converter<TKey,TValue>) | Adds a key/value pair to the IDictionary if the key does not already exist. | 
Target Platforms: Windows XP, Windows Server 2003, Windows Vista, Windows Server 2008, Windows 7