Implementing NSCopying in Subclass of Subclass

Question

I have a small class hierarchy that I\'m having trouble implementing copyWithZone: for. I\'ve read the NSCopying documentation, and I can\'t find the correct an

Answer 1

One of those things you realize right after asking...

The implementation of copyWithZone: in the superclass (Shape) shouldn't be assuming it's a Shape. So instead of the wrong way, as I mentioned above:

- (id)copyWithZone:(NSZone *)zone {
    Shape *s = [[Shape allocWithZone:zone] init];
    s.sides = self.sides;
    return s;
}

You should instead use:

- (id)copyWithZone:(NSZone *)zone {
    Shape *s = [[[self class] allocWithZone:zone] init]; // <-- NOTE CHANGE
    s.sides = self.sides;
    return s;
}