"normally domain should not be nil (you risk a crash in filters)" What should it be? "you get the same result, because of the cast as!." The same result as what? "Result is optional, but cannot be nil, it is forced unwrapped" If it cannot be nil, then why does it need to be optional? And why is it Any, and not 'actual' QuartzFilter? And what about the two different types of property? In your function, the result is a force unwrapped Any -- so why does it return an Optional? I guess this is just a complaint about the way that Apple has chosen to do things, which doesn't really seem to have any benefit, but I suppose I'll have to live with it. More exclamation marks!!!