オプショナル・チェイニング (Optional Chaining)

class Person {
	var residence: Residence?
}

class Residence {
	var numberOfRooms = 1
}

let john = Person()

let roomCount = john.residence?.numberOfRooms

let roomCount: Int?
if let residence = john.residence {
	roomCount = residence.numberOfRooms
} else {
	roomCount = nil
}