Hashing, and NSDictionaries

[Stephen Brandon]

Hi,

Just a query about the way NSDictionaries do their lookups.

It seems that although NSDictionary creates a hash of all keys handed to it, 
once it finds a match between a stored hash and the hash of a (possible) key 
sent to it, it then does an isEqual: between the stored key and the query key.

Why is this final equality check necessary? Isn't the fact that it already 
has a hash of the stored key and the query key, and the fact that they match, 
good enough?

In my situation, my -isEqual does a new hash of self and the other object and 
compares them -- so the number of hashes done can be very large! And there's 
quite a lot of redundant hashing going on.

Can anyone shed any light on this?

Cheers,
Stephen Brandon