We've been working with the quackologists for a while now and we just know that they're going to want more from us. We can imagine adding a flockID to the quackable objects and needing to query how many quackers are in a flock. There are certainly more things than we can imagine right now. We'd like to make it easy to add these, seemingly, ad hoc queries without a lot of effort. There's one more pattern that we'll add to our example. This is the Visitor pattern. The Visitor pattern is used when you want to add capabilities to a composite of objects and encapsulation is not important. We have composites, namely the flocks. So, we can build a IFlockVisitor interface that will gather information about the flocks.

The Visitor pattern looks like this: