HashTables in Cocoa

Question

HashTables/HashMaps are one of the most (if not the most) useful of data-structures in existence. As such, one of the first things I investigated when starting to learn programming in Cocoa was how to create, populate, and read data from a hashtable.

To my surprise: all the documentation I've been reading on Cocoa/Objective-C programming doesn't seem to explain this much at all. As a Java developer that uses "java.util" as if it were a bodily function: I am utterly baffled by this.

So, if someone could provide me with a primer for creating, populating, and reading the contents of a hashtable: I would greatly appreciate it.

Answer 1

NSDictionary and NSMutableDictionary?

And here's a simple example:

NSMutableDictionary *dictionary = [[NSMutableDictionary alloc] init];
[dictionary setObject:anObj forKey:@"foo"];
[dictionary objectForKey:@"foo"];
[dictionary removeObjectForKey:@"foo"];
[dictionary release];

Answer 2

If you're using Leopard (and Cocoa's new Garbage Collection), you also want to take a look at NSMapTable.

Answer 3

In addition to NSDictionary, also check out NSSet for when you need a collection with no order and no duplicates.