Question

I was wondering how keys work in a NSDictionary. Usually, I will use a NSString as a key for example:

NSString *stringKey = @"stringKey";
[mydict objectForKey:stringKey];

What if I wanted to use a NSNumber:

NSNumber *numberKey = [NSNumber numberWithInt:3];
[mydict objectForKey:numberKey];

Does the dictionary go look for the key with number 3? or would it just compare the address of the numberKey?

Answer 1

Two keys are equal if and only if [key1 isEqual:key2]. Some classes may go with the -[NSObject isEqual:] implementation of return self == other;, but it’s quite common for classes (such as NSString, NSNumber, etc) to override it to do more context-specific comparison.