CPLRUDictionary is a dictionary storing limited set of data, with extra data filted out by last accessed time. LRU stands for Least Recently Used [1].
CPLRUDictionary* dict = [[CPLRUDictionary alloc] initWithMaximumCapacity:4];
[dict setObject:@"1" forKey:@"first"];
[dict setObject:@"2" forKey:@"second"];
[dict setObject:@"3" forKey:@"third"];
[dict setObject:@"4" forKey:@"fourth"];
[dict objectForKey:@"first"]; // Bump "first" as most recently used.
[dict setObject:@"5" forKey:@"fifth"];
[dict setObject:@"6" forKey:@"sixth"];
NSLog(@"%@", [dict allKeys]); // Should have "first", "fourth", "fifth" and "sixth" in any order.
[dict release];