I suggested the use of UserDefaults.register(defaults:) today. During the conversation, I realized that this behaves very much like the Optional/Nil-Coalescing operator ??.

1. When UserDefaults have a stored value for a key, it’s like .some(...).
2. When UserDefaults don’t have a stored value for a key, the register(defaults:) collection is used as a fallback.
3. When UserDefaults don’t have a stored value for a key and there’s no registered default value, you get the system default for the given type – e.g. false for a boolean, or 0 for a number.

So for this call:

let value: Bool = UserDefaults.standard.bool(forKey: "i_can_has_cheezburger")

I imagine something like this happens:

boolFromApplicableDomains(forKey: "i_can_has_cheezburger") 
  ?? registeredDefaults["i_can_has_cheezburger"] as? Bool
  ?? Bool.defaultValue // => false