Repositories mimic a collection by implementing their common interface characteristics. As a collection, a Repository shouldn't leak any intentions of persistence behavior, such as the notion of saving to a store.
The underlying persistence mechanism has to support this need. You shouldn't be required to handle changes to the objects over their lifetime. The collection references the most recent changes to the object, meaning that upon each access, you get the latest object state.
Repositories implement a concrete collection type, the Set. A Set is a data structure with an invariant that doesn't contain duplicate entries. If you try to add an element that's already present to a Set, it won't be added. This ...
