Question

If I instantiate an NSArray passing it an NSMutableArray, does it become a NSArray or does it just appear to be one.

i.e. is the mutable array eventually released

- (NSArray *)getObjectivesWithPerspective:(Perspective *)perspective
{
    NSMutableArray *result = [NSMutableArray array];

    for (ObjectiveManagedObject *objective in self.objectives)
    {
        if (objective.perspective.objectID == perspective.objectID) {
            [result addObject:objective];
        }
    }

    return [NSArray arrayWithArray:result];
}

Answer 1

You can find some info about this here: what does -arrayWithArray actually DO?. But the array you get back should be immutable. NSArray will copy the references into an immutable array.

If in doubt do a test. Get an array back from the method, cast it as a NSMutableArray and try to add an object. You should get an error when you do this.