Objects as keys NSMutableDictionary

FROM : Matthias Winkelmann
DATE : Sun Jul 09 15:11:23 2006

I'm having a little problem with NSMutableDictionary and would like 
to find out what "best practice" for this is.

Here's a contrived example: A class "exam" should store the result 
for each student. So we have 20 students and an NSNumber for each. 
I'd like to store them like this:

in init:
NSMutableDictionary *result = [NSMutableDictionary dictionary];


- (void)setResult:(NSNumber *)aResult forStudent:(Student *)aStudent
{
   [results setObject:aResult forKey:aStudent];
}

Now firstly, NSDictionary likes NSStrings as keys for key-value 
coding. I don't depend on that, so I'm willing to ignore it. However, 
it also requires the keys to be immutable, so I'd have to copy the 
student object. I don't want to do that, since I want to later be 
able to go back and retrieve the result for that specific student.

I guess I could also store the results as an NSMutableArray of Result-
objects, but NSDictionary seems to be less overhead.

Thanks for any ideas,

m