What is the equivalent of Java's AbstractMap in C#?

Question

I need to create an object which exposes an IDictionary<K,V> interface, but I don't want to fill in the entire interface implemntation.

It would be nice to have the equivalent of Java's AbstractDictionary, which leaves you very little to impelment a complete dictionary (HashMap, in Java):

• If you don't need to iterate the collection, you have a single method to implement (TryGetValue)
• If you want it to be writeable, you implement another entry (Add).

Answer 1

System.Collections.Generic namespace contains three implementations of IDictionary<K,V>: Dictionary<TKey, TValue>, SortedDictionary<TKey, TValue> and SortedList<TKey, TValue>.

Answer 2

If I'm building my own dictionary class, I inherit from System.Collections.ObjectModel.KeyedCollection.

EDIT for all those who don't understand API design.

You should never, ever return a generic List or Dictionary from a public property or function. Insead you should return a class specially built for that purpose. This way you can add additional functionality to it later.

Dictionay<integer, Order> Orders() {get;}
CustomerOrders Orders() {get;}

With the second version you can do things like add a Total property and have the user actually find it.

In theory you could return a subclass of Dictionary that adds the Total property, but then the user would have to A. know you are doing it, and B. include a cast to get to the property.

Answer 3

Wintellect's PowerCollections library includes a DictionaryBase class (source code) that implements most of the standard IDictionary<K, V> interface. From the class' documentation comments:

DictionaryBase is a base class that can be used to more easily implement the generic IDictionary<T> and non-generic IDictionary interfaces.

To use DictionaryBase as a base class, the derived class must override Count, GetEnumerator, TryGetValue, Clear, Remove, and the indexer set accessor.