This week, we'll continue exploring various ways to implement the observer pattern in Swift. Last week we took a look at using the NotificationCenter API and observation protocols to enable an AudioPlayer to be observed, and this week we'll do the same thing but instead focusing on multiple closure-based techniques.

Often when building apps, we find ourselves in situations when we need to set up a one-to-many relationship between objects. In such situations, it's very common to want to add some way for certain objects to be observed. We'll start by taking a look at two such observation techniques this week, and then next week we'll continue with a couple of other ones.