An IdentityTable is a collection with indexes that can be any object. In an IdentityTable, each item is associated with a single index, and there can be only one item for each index. Index and item matches in an identity table are made using an object identity comparison. That is, an index will only match if the same instance is used in the collection.
The class IdentityTable subclasses (specializes) The Object Class and inherits (specializes) in addition: