Preferred way of returning an immutable object

Question

If I have a method that looks something like this:

- (NSDictionary *)removeDataInDictionary:(NSDictionary *)dictionary {

    NSMutableDictionary *mutableDictionary = [dictionary mutableCopy];
    [mutableDictionary removeObjectForKey:@"key"];

    // Return option 1
    return [NSDictionary dictionaryWithDictionary:mutableDictionary];

    // Return option 2
    return (NSDictionary *) mutableDictionary;
}

Is option 1 "better" codewise because it will really return a NSDictionary whilst option 2 will actually return a NSMutableDictionary disguised into a NSDictionary ?

Answer 1

The return option 1 will create an immutable NSDictionary object, which is the way to go if you don't want it to be edited by any means.

The return option 2 will return an NSMutableDictionary anyways. Casting it to a NSDictionary will not make any difference

HOWEVER: When calling this method, you will see that it returns an NSDictionary and thus you will have to consider it as such outside, so unless you check the object class and then cast it to an NSMutableDictionary outside your method, it will look immutable outside.