NSMutableDictionary key values

Question

is it true that the key values for NSMutableDictionary can only be strings?

I was trying to use objects, but I am getting a warning.

Answer 1

From the docs:

In general, a key can be any object (provided that it conforms to the NSCopying protocol—see below), but note that when using key-value coding the key must be a string (see Key-Value Coding Fundamentals).

What warning are you getting?

Answer 2

You can use any object, but the object must implement -[NSObject hash], -[NSObject isEqual:], and the NSCopying protocol.