Collections

Well, IDictionary inherits both ICollection and IEnumerable and so if your collection class implements IDictionary then it automatically implements the other two interfaces. However, there are still 8 properties and 8 methods to implement so there's still a fair amount of work to do.

In practice, it's unlikely that anyone would want to design their own class that implements IDictionary because the generic Dictionary, SortedDictionary and Hashtable classes in the .NET framework already do what most people want. 

However, there's an example of a custom class, SimpleDictionary, which implements IDictionary in the MSDN documentation (http://msdn.microsoft.com/en-us/library/system.collections.idictionary.aspx).